Assessment will usually include an interview with the child’s caregiver, observation of the child in an unstructured setting, a hearing test, and standardized tests of language. There is a wide range of language assessments in English. Some are restricted for use by experts in speech-language pathology: speech and language therapists (SaLTs/SLTs) in the UK, speech-language pathologists (SLPs) in the US and Australia. A commonly used test battery for diagnosis of DLD is the Clinical Evaluation of Language Fundamentals (CELF).

Assessments that can be completed by a parent or teacher can be useful to identify children who may require more in-depth evaluation. The Children’s Communication Checklist (CCC–2) is a parent questionnaire suitable for assessing everyday use of language in children aged 4 years and above who can speak in sentences.

Informal assessments, such as language samples, are often used by speech-language therapists/pathologists to complement formal testing and give an indication of the child's language in a more naturalistic context. A language sample may be of a conversation or narrative retell. In a narrative language sample, an adult may tell the child a story using a wordless picture book (e.g. Frog Where Are You?, Mayer, 1969), then ask the child to use the pictures and tell the story back. Language samples can be transcribed using computer software such as the Systematic Analysis of Language Software, and then analyzed for a range of features: e.g., the grammatical complexity of the child's utterances, whether the child introduces characters to their story or jumps right in, whether the events follow a logical order, and whether the narrative includes a main idea or theme and supporting details.

Assessment will usually include an interview with the child’s caregiver, observation of the child in an unstructured setting, a hearing test, and standardized tests of language and nonverbal ability. There is a wide range of language assessments in English. Some are restricted for use by speech and language professionals (therapists or SALTs in the UK, speech-language pathologists, SLPs, in the US and Australia).

A commonly used test battery for diagnosis of SLI is the Clinical Evaluation of Language Fundamentals (CELF).

Assessments that can be completed by a parent or teacher can be useful to identify children who may require more in-depth evaluation.

The Grammar and Phonology Screening (GAPS) test is a quick (ten minute) simple and accurate screening test developed and standardized in the UK. It is suitable for children from 3;4 to 6;8 years;months and can be administered by professionals and non-professionals (including parents) alike, and has been demonstrated to be highly accurate (98% accuracy) in identifying impaired children who need specialist help vs non-impaired children. This makes it potentially a feasible test for widespread screening.

The Children’s Communication Checklist (CCC–2) is a parent questionnaire suitable for testing language skills in school-aged children.

Informal assessments, such as language samples, may also be used. This procedure is useful when the normative sample of a given test is inappropriate for a given child, for instance, if the child is bilingual and the sample was of monolingual children. It is also an ecologically valid measure of all aspects of language (e.g. semantics, syntax, pragmatics, etc.).

To complete a language sample, the SLP will spend about 15 minutes talking with the child. The sample may be of a conversation (Hadley, 1998), or narrative retell. In a narrative language sample, the SLP will tell the child a story using a wordless picture book (e.g. "Frog Where Are You?", Mayer, 1969), then ask the child to use the pictures and tell the story back.

Language samples are typically transcribed using computer software such as the Systematic Analysis of Language Software (SALT, Miller et al. 2012), and then analyzed. For example, the SLP might look for whether the child introduces characters to their story or jumps right in, whether the events follow a logical order, and whether the narrative includes a main idea or theme and supporting details.

DLD is defined purely in behavioural terms: there is no biological test. There are three points that need to be met for a diagnosis of DLD:

1. The child has language difficulties that create obstacles to communication or learning in everyday life,

2. The child's language problems are unlikely to resolve by five years of age, and

3. The problems are not associated with a known biomedical condition such as brain injury, neurodegenerative conditions, genetic conditions or chromosome disorders such as Down Syndrome, sensorineural hearing loss, or Autism Spectrum Disorder or Intellectual Disability.

For research and epidemiological purposes, specific cutoffs on language assessments have been used to document the first criterion. Tomblin et al. proposed the EpiSLI criterion, based on five composite scores representing performance in three domains of language (vocabulary, grammar, and narration) and two modalities (comprehension and production). Children scoring in the lowest 10% on two or more composite scores are identified as having language disorder.

The second criterion, persistence of language problems, can be difficult to judge in a young child, but longitudinal studies have shown that difficulties are less likely to resolve for children who have poor language comprehension, rather than difficulties confined to expressive language. In addition, children with isolated difficulties in just one of the areas noted under 'subtypes' tend to make better progress than those whose language is impaired in several areas.

The third criterion specifies that DLD is used for children whose language disorder is not part of another biomedical condition, such as a genetic syndrome, a sensorineural hearing loss, neurological disease, Autism Spectrum Disorder or Intellectual Disability – these were termed 'differentiating conditions' by the CATALISE panel. Language disorders occurring with these conditions need to be assessed and children offered appropriate intervention, but a terminological distinction is made so that these cases would be diagnosed as Language Disorder associated with ___, with the main diagnosis being specified: e.g. "Language Disorder associated with Autism Spectrum Disorder." The reasoning behind these diagnostic distinctions is discussed further by Bishop (2017).

Many normed assessments can be used in evaluating skills in the primary academic domains: reading, including word recognition, fluency, and comprehension; mathematics, including computation and problem solving; and written expression, including handwriting, spelling and composition.

The most commonly used comprehensive achievement tests include the Woodcock-Johnson IV (WJ IV), Wechsler Individual Achievement Test II (WIAT II), the Wide Range Achievement Test III (WRAT III), and the Stanford Achievement Test–10th edition. These tests include measures of many academic domains that are reliable in identifying areas of difficulty.

In the reading domain, there are also specialized tests that can be used to obtain details about specific reading deficits. Assessments that measure multiple domains of reading include Gray's Diagnostic Reading Tests–2nd edition (GDRT II) and the Stanford Diagnostic Reading Assessment. Assessments that measure reading subskills include the Gray Oral Reading Test IV – Fourth Edition (GORT IV), Gray Silent Reading Test, Comprehensive Test of Phonological Processing (CTOPP), Tests of Oral Reading and Comprehension Skills (TORCS), Test of Reading Comprehension 3 (TORC-3), Test of Word Reading Efficiency (TOWRE), and the Test of Reading Fluency. A more comprehensive list of reading assessments may be obtained from the Southwest Educational Development Laboratory.

The purpose of assessment is to determine what is needed for intervention, which also requires consideration of contextual variables and whether there are comorbid disorders that must also be identified and treated, such as behavioral issues or language delays. These contextual variables are often assessed using parent and teacher questionnaire forms that rate the students' behaviors and compares them to standardized norms.

However, caution should be made when suspecting the person with a learning disability may also have dementia, especially as people with Down's syndrome may have the neuroanatomical profile but not the associated clinical signs and symptoms. Examination can be carried out of executive functioning as well as social and cognitive abilities but may need adaptation of standardized tests to take account of special needs.

Epidemiological surveys, in the US and Canada, estimated the prevalence of SLI in 5-year-olds at around 7 percent. However, neither study adopted the stringent 'discrepancy' criteria of the Diagnostic and Statistical Manual of Mental Disorders or ICD-10; SLI was diagnosed if the child scored below cut-off on standardized language tests, but had a nonverbal IQ of 90 or above and no other exclusionary criteria.

There are tests that can indicate with high probability whether a person is a dyslexic. If diagnostic testing indicates that a person may be dyslexic, such tests are often followed up with a full diagnostic assessment to determine the extent and nature of the disorder. Tests can be administered by a teacher or computer. Some test results indicate how to carry out teaching strategies.

Assessments for developmental coordination disorder typically require a developmental history, detailing ages at which significant developmental milestones, such as crawling and walking, occurred. Motor skills screening includes activities designed to indicate developmental coordination disorder, including balancing, physical sequencing, touch sensitivity, and variations on walking activities.

The American Psychiatric Association has four primary inclusive diagnostic criteria for determining if a child has developmental coordination disorder.

The criteria are as follows:

1. Motor Coordination will be greatly reduced, although the intelligence of the child is normal for the age.

2. The difficulties the child experiences with motor coordination or planning interfere with the child's daily life.

3. The difficulties with coordination are not due to any other medical condition

4. If the child does also experience comorbidities such as mental retardation; motor coordination is still disproportionally affected.

Screening tests which can be used to assess developmental coordination disorder include:-

- Movement Assessment Battery for Children (Movement-ABC – Movement-ABC 2)

- Peabody Developmental Motor Scales- Second Edition (PDMS-2)

- Bruininks-Oseretsky Test of Motor Proficiency (BOTMP-BOT-2)

- Motoriktest für vier- bis sechsjährige Kinder (MOT 4-6)

- Körperkoordinationtest für Kinder (KTK)

- Test of Gross Motor Development, Second Edition (TGMD-2)

- Maastrichtse Motoriek Test (MMT)

- Wechsler Adult Intelligence Scale (WAIS-IV)

- Wechsler Individual Achievement Test (WAIT-II)

- Test of Word Reading Efficiency (TOWRE-2)

- Developmental Coordination Disorder Questionnaire (DCD-Q)

- Children's Self-Perceptions of Adequacy in, and Predilection for Physical Activity (CSAPPA)

Currently there is no single gold standard assessment test.

A baseline motor assessment establishes the starting point for developmental intervention programs. Comparing children to normal rates of development may help to establish areas of significant difficulty.

However, research in the "British Journal of Special Education" has shown that knowledge is severely limited in many who should be trained to recognise and respond to various difficulties, including developmental coordination disorder, dyslexia and deficits in attention, motor control and perception (DAMP). The earlier that difficulties are noted and timely assessments occur, the quicker intervention can begin. A teacher or GP could miss a diagnosis if they are only applying a cursory knowledge.

"Teachers will not be able to recognise or accommodate the child with learning difficulties in class if their knowledge is limited. Similarly GPs will find it difficult to detect and appropriately refer children with learning difficulties."

Dyslexic children require special instruction for word analysis and spelling from an early age. While there are fonts that may help people with dyslexia better understand writing, this might simply be due to the added spacing between words. The prognosis, generally speaking, is positive for individuals who are identified in childhood and receive support from friends and family.

1. SCAN is the most common tool for diagnosing APD, and it also standardized. It is composed for four subsets: discrimination of monaurally presented single words against background noise, acoustically degraded single words, dichotically presented single words, sentence stimuli. Different versions of the test are used depending on the age of the patient.

2. Random Gap Detection Test (RGDT) is also a standardized test. It assesses an individual’s gap detection threshold of tones and white noise. The exam includes stimuli at four different frequencies (500, 1000, 2000, and 4000 Hz) and white noise clicks of 50 ms duration. It is a useful test because it provides an index of auditory temporal resolution. In children, an overall gap detection threshold greater than 20 ms means they have failed.

3. Gaps in Noise Test (GIN) also measures temporal resolution by testing the patient's gap detection threshold in white noise.

4. Pitch Patterns Sequence Test (PPT) and Duration Patterns Sequence Test (DPT) measure auditory pattern identification. The PPS has s series of three tones presented at either of two pitches (high or low). Meanwhile, the DPS has a series of three tones that vary in duration rather than pitch (long or short). Patients are then asked to describe the pattern of pitches presented.

Learning disabilities can be categorized by either the type of information processing affected by the disability or by the specific difficulties caused by a processing deficit.

According to the DSM-IV-TR, communication disorders are usually first diagnosed in childhood or adolescence though they are not limited as childhood disorders and may persist into adulthood. They may also occur with other disorders.

Diagnosis involves testing and evaluation during which it is determined if the scores/performance are "substantially below" developmental expectations and if they "significantly" interfere with academic achievement, social interactions and daily living. This assessment may also determine if the characteristic is deviant or delayed. Therefore, it may be possible for an individual to have communication challenges but not meet the criteria of being "substantially below" criteria of the DSM IV-TR.

It should also be noted that the DSM diagnoses do not comprise a complete list of all communication disorders, for example, auditory processing disorder is not classified under the DSM or ICD-10.

The following diagnoses are included in the communication disorders:

- Expressive language disorder – Characterized by difficulty expressing oneself beyond simple sentences and a limited vocabulary. An individual understands language better than their ability to use it; they may have a lot to say but have difficulties organizing and retrieving the words to get an idea across beyond what is expected for their developmental stage.

- Mixed receptive-expressive language disorder – problems comprehending the commands of others.

- Stuttering – a speech disorder characterized by a break in fluency, where sounds, syllables or words may be repeated or prolonged.

- Phonological disorder – a speech sound disorder characterized by problems in making patterns of sound errors, i.e. "dat" for "that".

- Communication disorder NOS (not otherwise specified) – the DSM-IV diagnosis in which disorders that do not meet the specific criteria for the disorder listed above may be classified.

Developmental coordination disorder is a lifelong neurological condition that is more common in males than in females, with a ratio of approximately four males to every female. The exact proportion of people with the disorder is unknown since the disorder can be difficult to detect due to a lack of specific laboratory tests, thus making diagnosis of the condition one of elimination of all other possible causes/diseases. Approximately 5–6% of children are affected by this condition.

It has been discovered that APD and ADHD present overlapping symptoms. Below is a ranked order of behavioral symptoms that are most frequently observed in each disorder. Professionals evaluated the overlap of symptoms between the two disorders. The order below is of symptoms that are almost always observed. This chart proves that although the symptoms listed are different, it is easy to get confused between many of them.

There is a high rate of co-occurrence between AD/HD and CAPD. Research shows that 84% of children with APD have confirmed or suspected ADHD. Co-occurrence between ADHD and APD is 41% for children with confirmed diagnosis of ADHD, and 43% for children suspected of having ADHD.

For nonverbal grade school children and adolescents with autism, communication systems and interventions have been implemented to enhance language and communication outcomes. Speech-generated devices, such as iPads, use visual displays for children who lack verbal language, giving them the task of selecting icons indicating a request or need. For adolescents with nonverbal autism, interventions can condition them to learn more advanced operations on speech-generated devices that require more steps (i.e. turning on device, scrolling through pages), which would allow them to enhance their communicative abilities independently.

The Picture Exchange System (PECS) is an alternative form of spontaneous communication for children with autism in which an individual selects a picture indicating a request. PECS can be utilized in educational settings and at the child’s home. Longitudinal studies suggest PECS can have long-term positive outcomes for school-aged children with nonverbal autism, specifically their social-communicative skills, such as higher frequencies of joint attention and initiation, and duration of cooperative play, which are all important roles in improving language outcomes.

It has also been suggested that a significant stage in acquiring verbal language is learning how to identify and reproduce syllables of words. One study found that nonverbal and minimally verbal children with autism are capable of enhancing their oral production and vocalizing written words by isolating each syllable of a word one at a time. The process of breaking down a syllable at a time and having it visually displayed and audibly available to the child can prompt him or her to imitate and create nonrandom and meaningful utterances.

Most of these studies contain small sample sizes and were pilot studies, making additional research significant to assess whether these findings can be generalized to all age groups of the same population. Furthermore, most studies on nonverbal autism speech-generated device communication were based on more basic skills, such as naming pictures and making requests for stimuli, while studies in advanced communication (i.e. asking "how are you?") is limited.

Another method implemented to test for aprosodia involves having questionnaires filled out by those close to the patient. The doctors and nurses taking care of a patient are also requested to fill out a questionnaire if aprosodia is suspected. This diagnosis method occurs more as an indicator that the aprosodia battery should be administered rather than being used as a singular diagnosis tool. Implementation of the questionnaire is expected to become more widespread as aprosodia is revealed to be a side-effect of more diseases.

About half of parents of children with ASD notice their child's unusual behaviors by age 18 months, and about four-fifths notice by age 24 months. According to an article, failure to meet any of the following milestones "is an absolute indication to proceed with further evaluations. Delay in referral for such testing may delay early diagnosis and treatment and affect the long-term outcome".

- No babbling by 12 months.

- No gesturing (pointing, waving, etc.) by 12 months.

- No single words by 16 months.

- No two-word (spontaneous, not just echolalic) phrases by 24 months.

- Any loss of any language or social skills, at any age.

The United States Preventive Services Task Force in 2016 found it was unclear if screening was beneficial or harmful among children in whom there is no concerns. The Japanese practice is to screen all children for ASD at 18 and 24 months, using autism-specific formal screening tests. In contrast, in the UK, children whose families or doctors recognize possible signs of autism are screened. It is not known which approach is more effective. Screening tools include the Modified Checklist for Autism in Toddlers (M-CHAT), the Early Screening of Autistic Traits Questionnaire, and the First Year Inventory; initial data on M-CHAT and its predecessor, the Checklist for Autism in Toddlers (CHAT), on children aged 18–30 months suggests that it is best used in a clinical setting and that it has low sensitivity (many false-negatives) but good specificity (few false-positives). It may be more accurate to precede these tests with a broadband screener that does not distinguish ASD from other developmental disorders. Screening tools designed for one culture's norms for behaviors like eye contact may be inappropriate for a different culture. Although genetic screening for autism is generally still impractical, it can be considered in some cases, such as children with neurological symptoms and dysmorphic features.

Pragmatic language impairment (PLI), or social (pragmatic) communication disorder (SCD), is an impairment in understanding pragmatic aspects of language. This type of impairment was previously called semantic-pragmatic disorder (SPD). People with these impairments have special challenges with the semantic aspect of language (the meaning of what is being said) and the pragmatics of language (using language appropriately in social situations). It is assumed that those with autism have difficulty with "the meaning of what is being said" due to different ways of responding to social situations.

PLI is now a diagnosis in DSM-5, and is called social (pragmatic) communication disorder. Communication problems are also part of the autism spectrum disorders (ASD); however, the latter also show a restricted pattern of behavior, according to behavioral psychology. The diagnosis SCD can only be given if ASD has been ruled out.

Classifying speech into normal and disordered is more problematic than it first seems. By a strict classification, only 5% to 10% of the population has a completely normal manner of speaking (with respect to all parameters) and healthy voice; all others suffer from one disorder or another.

There are three different levels of classification when determining the magnitude and type of a speech disorders and the proper treatment or therapy:

1. Sounds the patient can produce

1. Phonemic – can be produced easily; used meaningfully and constructively

2. Phonetic – produced only upon request; not used consistently, meaningfully, or constructively; not used in connected speech

2. Stimulate sounds

1. Easily stimulated

2. Stimulate after demonstration and probing (i.e. with a tongue depressor)

3. Cannot produce the sound

1. Cannot be produced voluntarily

2. No production ever observed

Disorders and tendencies included and excluded under the category of communication disorders may vary by source. For example, the definitions offered by the American Speech–Language–Hearing Association differ from that of the Diagnostic Statistical Manual 4th edition (DSM-IV).

Gleanson (2001) defines a communication disorder as a speech and language disorder which refers to problems in communication and in related areas such as oral motor function. The delays and disorders can range from simple sound substitution to the inability to understand or use their native language.

In general, communications disorders commonly refer to problems in speech (comprehension and/or expression) that significantly interfere with an individual’s achievement and/or quality of life. Knowing the operational definition of the agency performing an assessment or giving a diagnosis may help.

Persons who speak more than one language or are considered to have an accent in their location of residence do not have speech disorders if they are speaking in a manner consistent with their home environment or a blending of their home and foreign environment.

It is estimated that 25 to 50% of children diagnosed with Autism Spectrum Disorder (ASD) never develop spoken language beyond a few words or utterances. Despite the growing field of research on ASD, there is not much information available pertaining to individuals with autism who never develop functional language; that, in fact, individuals with nonverbal autism are considered to be underrepresented in all of autism research. Because of the limited research on nonverbal autism, there are not many validated measurements appropriate for this population. For example, while they may be appropriate for younger children, they lack the validity for grade-school aged children and adolescents and have continued to be a roadblock for nonverbal autism research. Often in autism research, individuals with nonverbal autism are sub-grouped with LFA, categorized by learning at most one word or having minimal verbal language.

Most of the existing body of research in nonverbal autism focuses on early interventions that predict successful language outcomes. Research suggests that most spoken language is inherited before the age of five, and the likelihood of acquiring functional language in the future past this age is minimal, that early language development is crucial to educational achievement, employment, independence during adulthood, and social relationships.

In most cases the cause is unknown. However, there are various known causes of speech impediments, such as "hearing loss, neurological disorders, brain injury, intellectual disability, drug abuse, physical impairments such as cleft lip and palate, and vocal abuse or misuse."

Children who demonstrate deficiencies early in their speech and language development are at risk for continued speech and language issues throughout later childhood. Similarly, even if these speech and language problems have been resolved, children with early language delay are more at risk for difficulties in phonological awareness, reading, and writing throughout their lives. Children with mixed receptive-expressive language disorder are often likely to have long-term implications for language development, literacy, behavior, social development, and even mental health problems. If suspected of having a mixed receptive-expressive language disorder, treatment is available from a speech therapist or pathologist. Most treatments are short term, and rely upon accommodations made within the environment, in order to minimize interfering with work or school. Programs that involve intervention planning that link verbal short term memory with visual/non-verbal information may be helpful for these children. In addition, approaches such as parent training for language stimulation and monitoring language through the "watch and see" method are recommended. The watch-and-see technique advises children with mixed receptive-expressive language disorder who come from stable, middle-class homes without any other behavioral, medical, or hearing problems should be vigilantly monitored rather than receive intervention. It is often the case that children do not meet the eligibility criteria established through a comprehensive oral language evaluation; and as a result, are not best suited for early intervention programs and require a different approach besides the "one size fits all" model.

In 1983, Rapin and Allen suggested the term "semantic pragmatic disorder" to describe the communicative behavior of children who presented traits such as pathological talkativeness, deficient access to vocabulary and discourse comprehension, atypical choice of terms and inappropriate conversational skills. They referred to a group of children who presented with mild autistic features and specific semantic pragmatic language problems. More recently, the term "pragmatic language impairment" (PLI) has been proposed.

Rapin and Allen's definition has been expanded and refined by therapists who include communication disorders that involve difficulty in understanding the meaning of words, grammar, syntax, prosody, eye gaze, body language, gestures, or social context. While autistic children exhibit pragmatic language impairment, this type of communication disorder can also be found in individuals with other types of disorders including auditory processing disorders, neuropathies, encephalopathies and certain genetic disorders.

While infection with rubella during pregnancy causes fewer than 1% of cases of autism, vaccination against rubella can prevent many of those cases.

In 2006, the U.S. Department of Education indicated that more than 1.4 million students were served in the public schools' special education programs under the speech or language impairment category of IDEA 2004. This estimate does not include children who have speech/language problems secondary to other conditions such as deafness; this means that if all cases of speech or language impairments were included in the estimates, this category of impairment would be the largest. Another source has estimated that communication disorders—a larger category, which also includes hearing disorders—affect one of every 10 people in the United States.

ASHA has cited that 24.1% of children in school in the fall of 2003 received services for speech or language disorders—this amounts to a total of 1,460,583 children between 3 –21 years of age. Again, this estimate does not include children who have speech/language problems secondary to other conditions. Additional ASHA prevalence figures have suggested the following:

- Stuttering affects approximately 4% to 5% of children between the ages of 2 and 4.

- ASHA has indicated that in 2006:

- Almost 69% of SLPs served individuals with fluency problems.

- Almost 29% of SLPs served individuals with voice or resonance disorders.

- Approximately 61% of speech-language pathologists in schools indicated that they served individuals with SLI

- Almost 91% of SLPs in schools indicated that they servedindividuals with phonological/articulation disorder

- Estimates for language difficulty in preschool children range from 2% to 19%.

- Specific Language Impairment (SLI) is extremely common in children, and affects about 7% of the childhood population.