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.

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.

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.

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.

Studies have failed to find clear evidence that language delay can be prevented by training or educating health care professionals in the subject. Overall, some of the reviews show positive results regarding interventions in language delay, but are not curative. (Commentary - Early Identification of Language Delays, 2005)

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.

After the initial diagnosis of speech delay, a hearing test will be administered to ensure that hearing loss or deafness is not an underlying cause of the delay. If a child has successfully completed the hearing test, the therapy or therapies used will be determined. There are many therapies available for children that have been diagnosed with a speech delay, and for every child, the treatment and therapies needed vary with the degree, severity, and cause of the delay. While speech therapy is the most common form of intervention, many children may benefit from additional help from occupational and physical therapies as well. Physical and occupational therapies can be used for a child that is suffering from speech delay due to physical malformations and children that have also been diagnosed with a developmental delay such as autism or a language processing delay. Children that have been identified with hearing loss can be taught simple sign language to build and improve their vocabulary in addition to attending speech therapy.

The parents of a delayed child are the first and most important tool in helping overcome the speech delay. The parent or caregiver of the child can provide the following activities at home, in addition to the techniques suggested by a speech therapist, to positively influence the growth of speech and vocabulary:

- Reading to the child regularly

- Use of questions and simple, clear language

- Positive reinforcement in addition to patience

For children that are suffering from physical disorder that is causing difficulty forming and pronouncing words, parents and caregivers suggest using and introducing different food textures to exercise and build jaw muscles while promoting new movements of the jaw while chewing. Another less studied technique used to combat and treat speech delay is a form of therapy using music to promote and facilitate speech and language development. It is important to understand that music therapy is in its infancy and has yet to be thoroughly studied and practiced on children suffering from speech delays and impediments.

In a typical 2-year-old child, about 50% of speech may be intelligible. A 4-year-old child's speech should be intelligible overall, and a 7-year-old should be able to clearly produce most words consistent with community norms for their age. Misarticulation of certain difficult sounds ("l", "r",

"s", "z", "th", "ch", "dzh", and "zh") may be normal up to 8 years. Children with speech sound disorder have pronunciation difficulties inappropriate for their age, and the difficulties are not caused by hearing problems, congenital deformities, motor disorders or selective mutism.

The DSM-5 diagnostic criteria are as follows:

- A. Persistent difficulty with speech sound production that interferes with speech intelligibility or prevents verbal communication of messages.

- B. The disturbance causes limitations in effective communication that interfere with social participation, academic achievement, or occupational performance, individually or in any combination.

- C. Onset of symptoms is in the early developmental period.

- D. The difficulties are not attributable to congenital or acquired conditions, such as cerebral palsy, cleft palate, deafness or hearing loss, traumatic brain injury, or other medical or neurological conditions.

For most children, the disorder is not lifelong and speech difficulties improve with time and speech-language treatment. Prognosis is poorer for children who also have a language disorder, as that may be indicative of a learning disorder.

Speech-language pathologists (SLPs) offer many services to children with speech or language disabilities.

Errors produced by children with speech sound disorders are typically classified into four categories:

- Omissions: Certain sounds are not produced — entire syllables or classes of sounds may be deleted; e.g., fi' for fish or 'at for cat.

- Additions (or Epentheses/Commissions): an extra sound or sounds are added to the intended word; e.g. puh-lane for plane.

- Distortions: Sounds are changed slightly so that the intended sound may be recognized but sounds "wrong," or may not sound like any sound in the language.

- Substitutions: One or more sounds are substituted for another; e.g., wabbit for rabbit or tow for cow.

Sometimes, even for experts, telling exactly which type has been made is not obvious — some distorted forms of /r/ may be mistaken for /w/ by a casual observer, yet may not actually be either sound but somewhere in between. Further, children with severe speech sound disorders may be difficult to understand, making it hard to tell what word was actually intended and thus what is actually wrong with it. Some terms can be used to describe more than one of the above categories, such as lisp, which is often the replacement of /s/ with /th/ (a substitution), but can be a distortion, producing /s/ just behind the teeth resulting in a sound somewhere between /s/ and /th/.

There are three different levels of classification when determining the magnitude and type of an error that is produced:

1. Sounds the patient can produce

1. A: Phonemic- can be produced easily; used meaningfully and contrastively

2. B: Phonetic- produced only upon request; not used consistently, meaningfully, or contrastively; not used in connected speech

2. Stimulable sounds

1. A: Easily stimulable

2. B: Stimulable after demonstration and probing (i.e. with a tongue depressor)

3. Cannot produce the sound

1. A: Cannot be produced voluntarily

2. B: No production ever observed

Note that omissions do not mean the sound cannot be produced, and some sounds may be produced more easily or frequently when appearing with certain other sounds: someone might be able to say "s" and "t" separately, but not "st," or may be able to produce a sound at the beginning of a word but not at the end. The magnitude of the problem will often vary between different sounds from the same speaker.

Speech delay, also known as alalia, refers to a delay in the development or use of the mechanisms that produce speech. Speech, as distinct from language, refers to the actual process of making sounds, using such organs and structures as the lungs, vocal cords, mouth, tongue, teeth, etc. Language delay refers to a delay in the development or use of the knowledge of language.

Because language and speech are two independent stages, they may be individually delayed. For example, a child may be delayed in speech (i.e., unable to produce intelligible speech sounds), but not delayed in language. In this case, the child would be attempting to produce an age appropriate amount of language, but that language would be difficult or impossible to understand. Conversely, since a child with a language delay typically has not yet had the opportunity to produce speech sounds, it is likely to have a delay in speech as well.

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.

Language delays are the most frequent developmental delays, and can occur for many reasons. A delay can be due to being a “late bloomer,” or a more serious problem. The most common causes of speech delay include

- Hearing loss

- Slow development

- Intellectual Disability

Such delays can occur in conjunction with a lack of mirroring of facial responses, unresponsiveness or unawareness of certain noises, a lack of interest in playing with other children or toys, or no pain response to stimuli.

Other causes include:

- Psychosocial deprivation - The child doesn't spend enough time talking with adults. Research on early brain development shows that babies and toddlers have a critical need for direct interactions with parents and other significant care givers for healthy brain growth and the development of appropriate social, emotional, and cognitive skills.

- Television viewing is associated with delayed language development. Children who watched television alone were 8.47 times more likely to have language delay when compared to children who interacted with their caregivers during television viewing. As recommended by the American Academy of Pediatrics (AAP), children under the age of 2 should watch no television at all, and after age 2 watch no more than one to two hours of quality programming a day. Therefore, exposing such young children to television programs should be discouraged. Parents should engage children in more conversational activities to avoid television-related delays to their children language development, which could impair their intellectual performance.

- Stress during pregnancy is associated with language delay.

- Being a twin

- Attention deficit hyperactivity disorder

- Autism (a developmental disorder) - There is strong evidence that autism is commonly associated with language delay. Asperger syndrome, which is on the autistic spectrum, however, is not associated with language delay.

- Selective mutism (the child just doesn't want to talk)

- Cerebral palsy (a movement disorder caused by brain damage)

- Genetic abnormalities - In 2005, researchers found a connection between expressive language delay and a genetic abnormality: a duplicate set of the same genes that are missing in sufferers of Williams-Beuren syndrome. Also so called XYY syndrome can often cause speech delay.

- Correlation with male sex, previous family history, and maternal education has been demonstrated.

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.

Muteness or mutism () is an inability to speak, often caused by a speech disorder, hearing loss, or surgery. Someone who is mute may be so due to the unwillingness to speak in certain social situations.

Expressive language disorder is a communication disorder in which there are difficulties with verbal and written expression. It is a specific language impairment characterized by an ability to use expressive spoken language that is markedly below the appropriate level for the mental age, but with a language comprehension that is within normal limits. There can be problems with vocabulary, producing complex sentences, and remembering words, and there may or may not be abnormalities in articulation.

As well as present speech production, very often, someone will have difficulty remembering things. This memory problem is only disturbing for speech; non-verbal or non-linguistically based memory will be unimpaired. An example of a child with expressive language disorder can be seen here.

Expressive language disorder affects work and schooling in many ways. It is usually treated by specific speech therapy, and usually cannot be expected to go away on its own.

Expressive language disorder can be further classified into two groups: developmental expressive language disorder and acquired expressive language disorder. Developmental expressive language disorder currently has no known cause, is first observed when a child is learning to talk, is more common in boys than girls, and is much more common than the acquired form of the disorder. Acquired expressive language disorder is caused by specific damage to the brain by a stroke, traumatic brain injury, or seizures.

Care must be taken to distinguish expressive language disorder from other communication disorders, sensory-motor disturbances, intellectual disability and/or environmental deprivation (see DSM-IV-TR criterion D). These factors affect a person's speech and writing to certain predictable extents, and with certain differences.

Careful diagnosis is also important because "atypical language development can be a secondary characteristic of other physical and developmental problems that may first manifest as language problems".

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.

An expressive language disability or delay in kindergarten age children is classified as a Communication Disability/Delay under a Code 30. If there is no marked improvement in the child's ability to express themselves verbally once the student enters Grade 1, a child can be given a Code 57 for a Communication Disability. This diagnosis must be given from a Speech-Language Pathologist in order for the child to receive continued special education funding.

Those who are physically mute may have problems with the parts of the human body required for human speech (the esophagus, vocal cords, lungs, mouth, or tongue, etc.).

Trauma or injury to Broca's area, located in the left inferior frontal cortex of the brain, can cause muteness.

Mixed receptive-expressive language disorder (DSM-IV 315.32) is a communication disorder in which both the receptive and expressive areas of communication may be affected in any degree, from mild to severe. Children with this disorder have difficulty understanding words and sentences. This impairment is classified by deficiencies in expressive and receptive language development that is not attributed to sensory deficits, nonverbal intellectual deficits, a neurological condition, environmental deprivation or psychiatric impairments. Research illustrates that 2% to 4% of 5 year olds have mixed receptive-expressive language disorder. This distinction is made when children have issues in expressive language skills, the production of language, and when children also have issues in receptive language skills, the understanding of language. Those with mixed receptive-language disorder have a normal left-right anatomical asymmetry of the planum temporale and parietale. This is attributed to a reduced left hemisphere functional specialization for language. Taken from a measure of cerebral blood flow (SPECT) in phonemic discrimination tasks, children with mixed receptive-expressive language disorder do not exhibit the expected predominant left hemisphere activation. Mixed receptive-expressive language disorder is also known as receptive-expressive language impairment (RELI) or receptive language disorder.

Hyperlexia is a syndrome characterized by a child's precocious ability to read. It was initially identified by Norman E. Silberberg and Margaret C. Silberberg (1967), who defined it as the precocious ability to read words without prior training in learning to read, typically before the age of 5. They indicated that children with hyperlexia have a significantly higher word-decoding ability than their reading comprehension levels. Children with hyperlexia also present with an intense fascination for written material at a very early age.

Hyperlexic children are characterized by having average or above-average IQs, and word-reading ability well above what would be expected given their age. First named and scientifically described in 1967 (Silverberg and Silverberg), it can be viewed as a superability in which word recognition ability goes far above expected levels of skill. Some hyperlexics, however, have trouble understanding speech. Some experts believe that most, or perhaps all children with hyperlexia, lie on the autism spectrum. However, one expert, Darold Treffert, proposes that hyperlexia has subtypes, only some of which overlap with autism. Between 5 and 20 percent of autistic children have been estimated to be hyperlexic.

Hyperlexic children are often fascinated by letters or numbers. They are extremely good at decoding language and thus often become very early readers. Some hyperlexic children learn to spell long words (such as "elephant") before they are two years old and learn to read whole sentences before they turn three.

An fMRI study of a single child showed that hyperlexia may be the neurological opposite of dyslexia.

Echolalia (also known as echologia or echophrasia) is defined as the unsolicited repetition of vocalizations made by another person (by the same person is called palilalia). In its profound form it is automatic and effortless. It is one of the echophenomena, closely related to echopraxia, the automatic repetition of movements made by another person; both are "subsets of imitative behavior" whereby sounds or actions are imitated "without explicit awareness". Echolalia may be an immediate reaction to a stimulus or may be delayed.

The word "echolalia" is derived from the Greek , meaning "echo" or "to repeat", and ("laliá") meaning "speech" or "talk" (of onomatopoeic origin, from the verb ("laléo"), meaning "to talk").

In psychiatry, stilted speech or pedantic speech is communication characterized by situationally inappropriate formality. This formality can be expressed both through abnormal prosody as well as speech content that is "inappropriately pompous, legalistic, philosophical, or quaint". Often, such speech can act as evidence for autism spectrum disorder (ASD) or a thought disorder, a common symptom in schizophrenia or schizotypal personality disorder.

To diagnose stilted speech, researchers have previously looked for the following characteristics:

- speech conveying more information than necessary

- vocabulary and grammar expected from formal writing rather than conversational speech

- unneeded repetition or corrections

While literal and long-winded word content is often the most identifiable feature of stilted speech, such speech often displays irregular prosody, especially in resonance. Often, the loudness, pitch, rate, and nasality of pedantic speech vary from normal speech, resulting in the perception of pedantic or stilted speaking. For example, overly loud or high-pitched speech can come across to listeners as overly forceful while slow or nasal speech creates an impression of condescension.

These attributions, which are commonly found in patients with ASD, partially account for why stilted speech has been considered a diagnostic criteria for the disorder. Stilted speech, along with atypical intonation, semantic drift, terseness, and perseveration, are all qualities known to be commonly impaired during conversation with adolescents on the autistic spectrum. Often, stilted speech found in children with ASD will also be especially stereotypic or rehearsed.

Patients with schizophrenia are also known to experience stilted speech. This symptom is attributed to both an inability to access more commonly used words and a difficulty understanding pragmatics, or the relationship between language and context. However, stilted speech appears as less common symptom compared to a certain number of other symptoms of the psychosis (Adler "et al" 1999). This element of cognitive disorder is also exhibited as a symptom in the narcissistic personality disorder (Akhtar & Thomson 1982).

In its more common usage, "stilted speech" is a term used to describe overly-formal, unnatural-sounding speech.

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.

Cluttering (also called tachyphemia or tachyphrasia) is a speech and communication disorder characterized by a rapid rate of speech, erratic rhythm, and poor syntax or grammar, making speech difficult to understand.