Hypernasality is generally segmented into so-called 'resonance' effects in vowels and some voiced or sonorant consonants and the effects of excess nasal airflow during those consonants requiring a buildup of oral air pressure, such as stop consonants (as /p/) or sibilants (as /s/). The latter nasal airflow problem is termed 'nasal emission', and acts to prevent the buildup of air pressure and thus prevent the normal production of the consonant. In testing for resonance effects without the aid of technology, speech pathologists are asked to rate the speech by listening to a recorded sentence or paragraph, though there is much variability in such subjective ratings, for at least two reasons. First, the acoustic effect of a given velopharyngeal opening varies greatly depending on the degree of occlusion of the nasal passageways. (This is the reason why a stuffy nose from an allergy or cold will sound more nasal than when the nose is clear.) Secondly, for many persons with hypernasal speech, especially hearing impaired, there are also mispronunciations of the articulation of the vowels. It is extremely difficult to separate the acoustic effects of hypernasality from the acoustic effects of mispronounced vowels (examples). Of course, in speech training of the hearing impaired, there is little possibility of making nasality judgments aurally, and holding a finger to the side of the nose, to feel voice frequency vibration, is sometimes recommended.

There are several methods for diagnosing hypernasality.

- A speech therapist listens to and records the child while analysing perceptual speech. In hypernasality, the child cannot produce oral sounds (vowels and consonants) correctly. Only the nasal sounds can be correctly produced. A hearing test is also desirable.

- A mirror is held beneath the nose while the child pronounces the vowels. Nasal air escape, and thus hypernasality, is indicated if the mirror fogs up.

- A pressure-flow technique is used to measure velopharyngeal orifice area during the speech. The patient must be at least three to four years old.

- A video nasopharyngeal endoscopy observes velopharyngeal function, movements of the soft palate, and pharyngeal walls. It utilises a very small scope placed in the back of the nasal cavity. The doctor will then ask the child to say a few words. The patient must be at least three to four years old to ensure cooperation.

- A cinefluoroscopy gives dynamic visualisation and can easier be applied to younger children, though it has the disadvantage of exposing the patient to radiation.

- A nasometer calculates the ratio of nasality. The patient wears a headset, where the oral and nasal cavities are separated by a plate. On both sides of the plate are microphones. The ratio calculated by the nasometer indicates the amount of nasality, with a higher ratio indicating more nasality.

A relatively new approach in the diagnosis is magnetic resonance imaging (MRI), which is noninvasive. MRI uses the property of nuclear magnetic resonance to image nuclei of atoms inside the body. MRI is non-radiographic and therefore can be repeated more often in short periods of time. In addition, different studies show that the MRI is better as a diagnostic tool than videofluoroscopy for visualizing the anatomy of the velopharynx.

On the contrary there are still a few limitations of the MRI. Firstly, artifacts can be shown on the images when the patient moves while imaging. Also artifacts will also be shown if the patient has orthodontic appliances. Secondly, the MRI is limited in children who are claustrophobic.

Furthermore, in the MRI scanner movement of the sphincter leads to artifacts on the images. Therefore, nasoendoscopy is still needed for information about the sphincter’s movement. Finally, the MRI is a more expensive diagnostic tool than the combination of nasoendoscopy and videofluoroscopy.

Because of these limits, MRI is currently not widely used. Overall, MRI is used for a “bird's eye view” of the child in the planning of the operation, but not in the progress of diagnosis.

Multiview videofluoroscopy is a radiographic technique, mostly to demonstrate the lateral and posterior wall of the pharynx. This is a questionable technique considering these children undergo radiographic examinations frequently. Also known is that children are more sensitive to radiographic examinations than adults. Most of the time barium is used in multiview videofluoroscopy. Besides the fact that videofluoroscopy provides an overview of the lateral and posterior walls of the pharynx, this technique also provides information about the length and movement of the soft palate, the posterior and the lateral walls.

A limitation of multiview videofluoroscopy is the possibility of misinterpreting certain shapes of gaps and anatomic structures.

The most frequently used diagnostic tools are videofluoroscopy and nasoendoscopy. Some studies conclude that the first step in the process of diagnosis is videofluoroscopy in combination with nasometry. Other studies show a favour for nasoendoscopy. But in general there is no preference for which tool should be used as a standard. Most studies conclude that it is necessary to make an individual decision on which diagnostic tool should be used.

To determine whether a client presents with puberphonia, a complete voice assessment including medical and diagnostic evaluations is recommended. These assessments are performed by otorhinolaryngologists and speech-language pathologists.

A behavioural assessment for puberphonia will consist of several types of tasks, and may include:

- Examining for tension in the neck and throat: The clinician will visually examine the area around the larynx to see if the voice box sits high in the throat, and palpate the area to determine whether there is excessive muscular tension.

- Determining the relationship between tension and vocal pitch: The clinician will ask the client to perform warm-up and relaxation exercises such as those listed in the Treatment section below to determine whether the client has access to their modal voice register.

- Establishing vocal range: The clinician will ask the client to produce the lowest and highest pitch that they can, and perform different speaking or singing activities at various pitches.

- Listening for abnormal traits: The clinician will listen for the presence of breathy voice, an indication of speech in the falsetto register, and other distortions of vocal quality.

- Taking aerodynamic measurements: Many individuals with puberphonia may have limited breath support caused by the thoracic or shallow breathing patterns often used to support speech in the falsetto register. These symptoms are assessed using vocal tasks such as maximum phonation time and direct measures of breath support such as glottal airflow and subglottal pressure.

Developmental Verbal Dyspraxia can be diagnosed by a speech language pathologist (SLP) through specific exams that measure oral mechanisms of speech. The oral mechanisms exam involves tasks such as pursing lips, blowing, licking lips, elevating the tongue, and also involves an examination of the mouth. A complete exam also involves observation of the patient eating and talking. Tests such as the Kaufman Speech Praxis test, a more formal examination, are also used in diagnosis.

A differential diagnosis of DVD/CAS is often not possible for children under the age of 2 years old. Even when children are between 2–3 years, a clear diagnosis cannot always occur, because at this age, they may still be unable to focus on, or cooperate with, diagnostic testing.

With an interdental lisp, the therapist teaches the child how to keep the tongue behind the two front incisors.

One popular method of correcting articulation or lisp disorders is to isolate sounds and work on correcting the sound in isolation. The basic sound, or phoneme, is selected as a target for treatment. Typically the position of the sound within a word is considered and targeted. The sound appears in the beginning of the word, middle, or end of the word (initial, medial, or final).

Take for example, correction of an "S" sound (lisp). Most likely, a speech language pathologist (SLP) would employ exercises to work on "Sssssss." Starting practice words would most likely consist of "S-initial" words such as "say, sun, soap, sip, sick, said, sail." According to this protocol, the SLP slowly increases the complexity of tasks (context of pronunciations) as the production of the sound improves. Examples of increased complexity could include saying words in phrases and sentences, saying longer multi syllabic words, or increasing the tempo of pronunciation.

Using this method, the SLP achieves success with his/her student by targeting a sound in a phonetically consistent manner. Phonetic consistency means that a target sound is isolated at the smallest possible level (phoneme, phone, or allophone) and that the context of production must be consistent. Consistency is critical, because factors such as the position within the word, grouping with other sounds (vowels or consonants), and the complexity all may affect production.

Another popular method for treating a lisp is using specially designed devices that go in the mouth to provide a tactile cue of exactly where the tongue should be positioned when saying the "S" sound. This tactile feedback has been shown to correct lisp errors twice as fast as traditional therapy.

Using either or both methods, the repetition of consistent contexts allows the student to align all the necessary processes required to properly produce language; language skills (ability to formulate correct sounds in the brain: What sounds do I need to make?), motor planning (voicing and jaw and tongue movements: How do I produce the sound?), and auditory processing (receptive feedback: Was the sound produced correctly? Do I need to correct?).

A student with an articulation or lisp disorder has a deficiency in one or more of these areas. To correct the deficiency, adjustments have to be made in one or more of these processes. The process to correct it is more often than not, trial and error. With so many factors, however, isolating the variables (the sound) is imperative to getting to the end result faster.

A phonetically consistent treatment strategy means practicing the same thing over and over. What is practiced is consistent and does not change. The words might change, but the phoneme and its positioning is the same (say, sip, sill, soap, …). Thus, successful correction of the disorder is found in manipulating or changing the other factors involved with speech production (tongue positioning, cerebral processing, etc.). Once a successful result (speech) is achieved, then consistent practice becomes essential to reinforcing correct productions.

When the difficult sound is mastered, the child will then learn to say the sound in syllables, then words, then phrases and then sentences. When a child can speak a whole sentence without lisping, attention is then focused on making correct sounds throughout natural conversation. Towards the end of the course of therapy, the child will be taught how to monitor his or her own speech, and how to correct as necessary. Speech therapy can sometimes fix the problem, but however in some cases speech therapy fails to work.

Permanent lisps can often be corrected through extensive oral operations. Often, when a patient has extreme overbite, causing a lisp, having orthodontic braces and rubber bands for an extended period of time will correct the issue, and resolve the lisp.

There are varying types of intervention for ankyloglossia. Horton "et al.," have a classical belief that people with ankyloglossia can compensate in their speech for limited tongue range of motion. For example, if the tip of the tongue is restricted for making sounds such as /n, t, d, l/, the tongue can compensate through dentalization; this is when the tongue tip moves forward and up. When producing /r/, elevation of the mandible can compensate for restriction of tongue movement. Also, compensations can be made for /s/ and /z/ by using the dorsum of the tongue for contact against the palatal rugae. Thus, Horton "et al." proposed compensatory strategies as a way to counteract the adverse effects of ankyloglossia and did not promote surgery. Non-surgical treatments for ankyglossia are typically performed by Orofacial Myology specialists, and involve using exercises to strengthen and improve the function of the facial muscles and thus promote proper function of the face, mouth and tongue

Intervention for ankyloglossia does sometimes include surgery in the form of frenotomy (also called a frenectomy or frenulectomy) or frenuloplasty. This relatively common dental procedure may be done with soft-tissue lasers, such as the CO laser. However, authors such as Horton "et al." are in opposition to it. According to Lalakea and Messner, surgery can be considered for patients of any age with a tight frenulum, as well as a history of speech, feeding, or mechanical/social difficulties. Adults with ankyloglossia may elect the procedure. Some of those who have done so report post-operative pain.

A viable alternative to surgery for children with ankyloglossia is to take a wait-and-see approach. Ruffoli "et al." report that the frenulum naturally recedes during the process of a child's growth between six months and six years of age;

According to Horton "et al.", diagnosis of ankyloglossia may be difficult; it is not always apparent by looking at the underside of the tongue, but is often dependent on the range of movement permitted by the genioglossus muscles. For infants, passively elevating the tongue tip with a tongue depressor may reveal the problem. For older children, making the tongue move to its maximum range will demonstrate the tongue tip restriction. In addition, palpation of genioglossus on the underside of the tongue will aid in confirming the diagnosis.

A severity scale for ankyloglossia, which grades the appearance and function of the tongue, is recommended for use in the Academy of Breastfeeding medicine.

A number of operations that cut one of the nerves of the vocal folds (the recurrent laryngeal nerve) has improved the voice of many for several months to several years but the improvement may be temporary.

An operation called "selective laryngeal adductor denervation-rennervation (SLAD-R)" is effective specifically for adductor spasmodic dysphonia which has shown good outcomes in about 80% of people at 8 years. Post-surgery voices can be imperfect and about 15% of people have significant difficulties. If symptoms do recur this is typically in the first 12 months. Another operation called "recurrent laryngeal nerve avulsion" has positive outcomes of 80% at three years.

Another surgical option is a thyroplasty, which ultimately changes the position or length of the vocal folds. After thyroplasty there is an increase in both objective and subjective measures of speech.

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.

Traditionally, the diagnosis is made at the time of birth by physical examination. Recent advances in prenatal diagnosis have allowed obstetricians to diagnose facial clefts in utero with ultrasonography.

Clefts can also affect other parts of the face, such as the eyes, ears, nose, cheeks, and forehead. In 1976, Paul Tessier described fifteen lines of cleft. Most of these craniofacial clefts are even rarer and are frequently described as Tessier clefts using the numerical locator devised by Tessier.

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."

Sensory aphasia cannot be diagnosed through the use of imaging techniques. Differences in cognition between asymptomatic subjects and affected patients can be observed via functional magnetic resonance imaging (fMRI). However, these results only reveal temporal differences in cognition between control and diagnosed subjects. The degree of progression during therapy can also be surveyed through cognition tests monitored by fMRI. Many patients’ progress is assessed over time via repeated testing and corresponding cerebral imaging by fMRI.

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

Successful treatments have shown that causes are functional rather than physical: that is, most lisps are caused by errors in tongue placement within the mouth rather than caused by any injury or congenital deformity to the mouth. The most frequently discussed of these problems is tongue thrust in which the tongue protrudes beyond the front teeth. This protrusion affects speech as well as swallowing and can lead to lisping. Ankyloglossia or tongue tie can also be responsible for lisps in children.

However, it is unclear whether these deficiencies are caused by the tongue tie itself or the muscle weakness following the correction of the tongue tie. Overbites and underbites may also contribute to non lingual lisping. Temporary lisps can be caused by dental work, dental appliances such as dentures or retainers or by swollen or bruised tongues.

Voice therapy appears to be ineffective in cases of true spasmodic dysphonia, however as it is difficult to distinguish between spasmodic dysphonia and functional dysphonias and misdiagnosis is relatively common, a trial of voice therapy is often recommended before more invasive procedures are tried. Some also state that it is useful for mild symptoms and as an add-on to botox therapy and others report success in more severe cases. Laryngeal manual therapy, which is massaging of the neck and cervical structures, also shows positive results for intervention of functional dysphonia.

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.

Sensory aphasia is typically diagnosed by non-invasive evaluations. Neurologists, neuropsychologists or speech pathologists will administer oral evaluations to determine the extent of a patient’s comprehension and speech capability. Initial assessment will determine if the cause of linguistic deficiency is aphasia. If the diagnosis is then confirmed, testing will next address the type of aphasia and its severity. The Boston Diagnostic Aphasia Examination specializes in determining the severity of a sensory aphasia through the observation of conversational behaviors. Several modalities of perception and response are observed in conjunction with the subject’s ability to process sensory information. The location of the brain lesion and type of the aphasia can then be inferred from the observed symptoms. The Minnesota Test for Differential Diagnosis is the most lengthy and thorough assessment of sensory aphasia. It pinpoints weaknesses in the auditory and visual senses, as well as reading comprehension. From this differential diagnosis, a patient’s course of treatment can be determined. After treatment planning, the Porch Index of Communicative Ability is used to evaluate prognosis and the degree of recovery.

The U.S. Food and Drug Administration (FDA) has not approved any drug for the direct treatment of stuttering. However, the effectiveness of pharmacological agents, such as benzodiazepines, anticonvulsants, antidepressants, antipsychotic and antihypertensive medications, and dopamine antagonists in the treatment of stuttering has been evaluated in studies involving both adults and children.

A comprehensive review of pharmacological treatments of stuttering in 2006 concluded that few of the drug trials were methodologically sound. Of those that were, only one, not unflawed study, showed a reduction in the frequency of stuttering to less than 5% of words spoken. In addition, potentially serious side effects of pharmacological treatments were noted, such as weight gain, sexual dysfunctions and the potential for blood pressure increases. There is one new drug studied especially for stuttering named pagoclone, which was found to be well-tolerated "with only minor side-effects of headache and fatigue reported in a minority of those treated".

Individuals with conduction aphasia are able to express themselves fairly well, with some word finding and functional comprehension difficulty. Although people with aphasia may be able to express themselves fairly well, they tend to have issues repeating phrases, especially phrases that are long and complex. When asked to repeat something, the patient will be unable to do so without significant difficulty, repeatedly attempting to self-correct ("conduite d'approche"). When asked a question, however, patients can answer spontaneously and fluently.

Several standardized test batteries exist for diagnosing and classifying aphasias. These tests are capable of identifying conduction aphasia with relative accuracy. The Boston Diagnostic Aphasia Examination (BDAE) and the Western Aphasia Battery (WAB) are two commonly used test batteries for diagnosing conduction aphasia. These examinations involve a set of tests, which include asking patients to name pictures, read printed words, count aloud, and repeat words and non-words (such as "shwazel").

Research has shown that PC based spatial hearing training software can help some of the children identified as failing to develop their spatial hearing skills (perhaps because of frequent bouts of otitis media with effusion). Further research is needed to discover if a similar approach would help those over 60 to recover the loss of their spatial hearing. One such study showed that dichotic test scores for the left ear improved with daily training. Related research into the plasticity of white-matter (see Lövdén et al. for example) suggests some recovery may be possible.

Music training leads to superior understanding of speech in noise across age groups and musical experience protects against age-related degradation in neural timing. Unlike speech (fast temporal information), music (pitch information) is primarily processed by areas of the brain in the right hemisphere. Given that it seems likely that the right ear advantage (REA) for speech is present from birth, it would follow that a left ear advantage for music is also present from birth and that MOC efferent inhibition (of the right ear) plays a similar role in creating this advantage. Does greater exposure to music increase conscious control of cochlear gain and inhibition? Further research is needed to explore the apparent ability of music to promote an enhanced capability of speech in noise recognition.

Bilateral digital hearing aids do not preserve localization cues (see, for example, Van den Bogaert et al., 2006) This means that audiologists when fitting hearing aids to patients (with a mild to moderate age related loss) risk negatively impacting their spatial hearing capability. With those patients who feel that their lack of understanding of speech in background noise is their primary hearing difficulty then hearing aids may simply make their problem even worse - their spatial hearing gain will be reduced by in the region of 10 dB. Although further research is needed, there is a growing number of studies which have shown that open-fit hearing aids are better able to preserve localisation cues (see, for example, Alworth 2011)

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.

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.