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Speech sound disorders: types, features and how they differ

Bodour Imseeh, Speech and Language Therapist
BSc (Hons) Speech and Language Therapy · MSc Speech Difficulties
Last reviewed: 30 October 2026

On this page
  1. Classification at a glance
  2. The disorders
    1. Phonological delay
    2. Consistent atypical phonological disorder
    3. Inconsistent phonological disorder
    4. Articulation disorder
    5. Childhood apraxia of speech (CAS)
    6. Childhood dysarthria
    7. Cleft lip and palate, and velopharyngeal dysfunction
    8. Speech differences related to hearing loss
  3. Difference or disorder? Bilingual and dialect-aware assessment
  4. Printable: SSD Differential Comparison Chart
  5. References

A speech sound disorder (SSD) is any difficulty with perceiving, planning or producing the speech sounds of a language, or with the rules for how those sounds combine. It is one of the most common childhood communication difficulties: about 3.4% of 4-year-olds in a large community cohort met criteria for SSD, and 40.8% of them also had a language disorder (Eadie et al. 2015). For some children it persists: 3.6% of 8-year-olds in a UK population study still had an SSD (Wren et al. 2016).

There is no single agreed way to classify SSDs. Researchers classify by underlying basis, by error pattern, or by presumed origin. This page uses two complementary lenses. They answer different questions and are not one nested system:

  • ASHA’s framework sorts by underlying basis. Organic SSDs have an underlying motor/neurological, structural or sensory/perceptual basis, even when a specific cause is not identified. Functional SSDs have no identified basis.
  • Dodd’s Model for Differential Diagnosis sorts by error pattern into five subgroups: phonological delay, consistent atypical phonological disorder, inconsistent phonological disorder, articulation disorder and CAS. It has been tested in community samples and in several languages.

The two overlap but do not map neatly. Dodd’s four non-CAS subgroups generally align with functional SSD presentations, while ASHA classifies CAS as a motor speech disorder. The mapping is approximate, because presentation and underlying basis are different questions. Dodd’s model does not cover cleft or hearing-related speech differences.

A classification is a working description, not a box. Mixed presentations are common: children can meet criteria for more than one subtype, speech sound, language and motor speech difficulties often co-occur, and the picture can change over time.

This page is a reference, not a diagnostic tool. Diagnosis needs a comprehensive multilingual assessment by a qualified clinician, using appropriate methods for each language as far as feasible.

Classification at a glance

Speech sound disorders divide by whether there is an underlying basis. Organic: motor/neurological (childhood apraxia of speech, childhood dysarthria), structural (cleft lip and palate, VPD), sensory/perceptual (hearing-related speech differences). Functional: articulation disorder, and phonological disorders in Dodd's subgroups (phonological delay, consistent atypical, inconsistent). Dodd's fifth subgroup, CAS, is under Motor.

ASHA groups SSDs by whether there is an underlying motor, structural or sensory basis. Dodd’s subgroups describe error patterns and cut across that split: four generally align with functional SSD, and ASHA classifies CAS as motor.

The disorders

Each disorder below uses the same six headings so they can be compared directly. “How it’s identified” lists parts of a full assessment, not a stand-alone diagnostic procedure. A full assessment also looks beyond speech: broader language and, especially for phonological disorders, phonological awareness help interpret the child’s profile and plan intervention.

Functional SSDs (no identified underlying basis)

Phonological delay

  • What it is: the child uses the same error patterns as younger typically developing children, past the age they usually resolve. It is the largest subgroup, about 55% of children with SSD in a community cohort (Ttofari Eecen et al. 2019).
  • Key features: developmental patterns such as fronting, stopping, cluster reduction or weak syllable deletion; errors are consistent. Vowels and prosody are usually typical, though this is not a defining requirement.
  • Often confused with: consistent atypical phonological disorder (check for any non-developmental patterns) and typical bilingual development (check norms for each language).
  • Bilingual and dialect considerations: “Delayed” only means something against norms for the child’s own dialect. Arabic norms exist by dialect, for example Jordanian (Amayreh & Dyson 1998). A pattern may be age-appropriate in one language and late in the other.
  • How it’s identified: single-word naming and connected speech, error patterns compared with age norms for each language.
  • Next: compare in the differential tool · see approaches in the Approach Finder

Consistent atypical phonological disorder

  • What it is: consistent use of at least some error patterns that typically developing children rarely use at any age. About 20% of children with SSD (Ttofari Eecen et al. 2019).
  • Key features: patterns such as initial consonant deletion, backing, affrication of fricatives or vowel errors, alongside developmental ones (Dodd et al. 2023). Errors are predictable. Vowel errors on their own do not place a child in this subgroup.
  • Often confused with: phonological delay, and cross-language transfer that looks atypical against one language’s norms.
  • Bilingual and dialect considerations: “Atypical” is defined by each language’s norms. A pattern that is unusual in English may be expected in a dialect, or may be transfer. Similar unexpected patterns across languages may strengthen concern, but don’t establish a disorder on their own.
  • How it’s identified: phonological pattern analysis of single words, checked against norms for each language and dialect.
  • Next: compare in the differential tool · see approaches in the Approach Finder

Inconsistent phonological disorder

  • What it is: the child says the same word in different ways, with no signs of a motor speech disorder. Thought to reflect difficulty assembling a phonological plan for a word. About 15% of 4-year-olds with SSD in one community cohort (Ttofari Eecen et al. 2019), and 9.4% of 320 children with primary speech impairment referred to one UK service (Broomfield & Dodd 2004).
  • Key features: high inconsistency on repeated naming. On the DEAP Inconsistency Assessment, the criterion is 40% or more of 25 words produced differently across three trials. That is a criterion within one assessment, based on English-speaking norms. It is not a universal cut-off and is not validated for Arabic. Other possible signs, none of them required: default sounds (for example [h] or [d] for many consonants), errors in word structure and sound order, and, in some children, fewer errors when imitating (Dodd et al. 2023). In English normative data, typically developing children over 3;6 produced fewer than 10% of words inconsistently (Holm et al. 2007, cited in Dodd et al. 2023).
  • Often confused with: CAS. Both can show inconsistent productions (mean inconsistency 58–64% in CAS groups and 56–58% in inconsistent phonological disorder groups, in studies reviewed by Dodd et al. 2023), so inconsistency alone cannot separate them. Word length does not separate them either: in inconsistent phonological disorder, inconsistency can also increase with more phonemes, syllables and clusters; in one study, simple one-syllable words were produced most consistently. Typical DDK, oromotor skills and prosody fit inconsistent phonological disorder better than CAS, but no single task rules CAS in or out; the decision rests on converging evidence (Dodd et al. 2023).
  • Bilingual and dialect considerations: Count inconsistency within one language only. Switching to the translation equivalent, or alternating between dialect and Standard Arabic forms of a word, is not inconsistency. The 40% criterion and the under-10% norm come from English-speaking children, so treat them as a guide rather than a threshold in other languages.
  • How it’s identified: inconsistency assessment (the same words named three times in one session), plus oromotor and DDK checks.
  • Next: compare in the differential tool · see approaches in the Approach Finder

Articulation disorder

  • What it is: difficulty producing specific speech sounds accurately, at the phonetic level, rather than a problem with the sound system (ASHA). Can occur alongside a phonological disorder.
  • Key features: relatively stable difficulty producing specific sounds, usually distortions or substitutions (for example, an interdental /s/). The difficulty is phonetic: it lies in producing the sound, not in rule-based patterns that affect a whole class of sounds, as in phonological disorders. Errors can still vary with phonetic context, word position and word complexity, and stimulability varies.
  • Often confused with: phonological disorder (ASHA notes the two are often impossible to separate fully) and accent.
  • Bilingual and dialect considerations: A sound that exists in only one language may be produced with the features of the other. This is usually accent or transfer rather than disorder. A distortion of a sound shared by both languages, appearing in both, is more likely to be an articulation difficulty.
  • How it’s identified: sound-by-sound production across positions, with stimulability testing.
  • Next: compare in the differential tool · see approaches in the Approach Finder

Organic SSDs (underlying motor, structural or sensory basis)

Childhood apraxia of speech (CAS)

  • What it is: a neurological disorder of planning and programming speech movements, without muscle weakness. ASHA describes it as occurring with known neurological impairment, with complex neurobehavioural disorders, or as an idiopathic neurogenic disorder, so many children have no identified cause (ASHA 2007). Uncommon: about 2.4% of 415 children with idiopathic speech delay met CAS criteria in one sample (Shriberg et al. 2019).
  • Key features: ASHA’s three consensus features: inconsistent errors on consonants and vowels across repeated productions; lengthened, disrupted transitions between sounds and syllables; inappropriate prosody, especially stress (Chenausky et al. 2020). ASHA notes these are not individually diagnostic, and they are not a validated checklist. In one study of children referred with suspected CAS, four measures together (syllable segregation, lexical stress matches, accuracy on polysyllables and on /pətəkə/) agreed with expert diagnosis in about 91% of cases (Murray et al. 2015). That is agreement with expert judgement in one sample, not a diagnostic cut-off.
  • Often confused with: inconsistent phonological disorder, severe phonological disorder, and dysarthria. There are still no evidence-based markers that reliably separate CAS from all other SSDs (Murray et al. 2021), so diagnosis rests on converging evidence across tasks. No single task, including DDK, confirms or excludes CAS. Use caution under age 3, when vowel errors and inconsistency are still common.
  • Bilingual and dialect considerations: The underlying motor planning difficulty is expected across languages, but how it shows, and how severe it looks, can vary with each language’s demands and the child’s proficiency. Judge vowel errors against each language’s vowel system, stress against each language’s stress patterns, and inconsistency within a language.
  • How it’s identified: repeated productions of the same words, polysyllabic words, DDK including sequences, stress and prosody in connected speech, in each language as far as feasible.
  • Next: compare in the differential tool · see approaches in the Approach Finder

Childhood dysarthria

  • What it is: a neuromotor speech disorder affecting the strength, speed, range, tone, steadiness or coordination of speech movements. It may occur with neurological conditions such as cerebral palsy, or other conditions affecting neuromuscular control of speech.
  • Key features: slow, laboured, imprecise articulation; sound prolongations; irregular pausing (ASHA). Breathing, voice, resonance, articulation and prosody may be affected. Errors are usually more consistent than in CAS.
  • Often confused with: CAS. The two can co-occur and share features, so subsystem assessment is essential (Iuzzini-Seigel et al. 2022).
  • Bilingual and dialect considerations: The underlying neuromotor difficulty is expected across languages, but how it shows, and how severe it sounds, can vary with each language’s demands and the child’s proficiency.
  • How it’s identified: oromotor examination, assessment of each speech subsystem, and connected speech.
  • Next: compare in the differential tool · see approaches in the Approach Finder

Cleft lip and palate, and velopharyngeal dysfunction

  • What it is: speech differences linked to the lip, palate or velopharyngeal valve, whether the problem is structural, neuromotor or learned.
  • Key features: two kinds of feature that need separating (ASHA). Structural features come from the palate or valve itself and may include hypernasality, reduced oral pressure and nasal air emission; not every child shows all three. Compensatory errors are learned: for example, glottal stops for stops and pharyngeal fricatives for sibilants. Management depends on the mechanism: structural insufficiency usually needs surgical or prosthetic management; neuromotor incompetence needs medical and speech assessment to decide; learned misarticulation, including compensatory errors, needs speech therapy and can persist after surgery.
  • Often confused with: articulation or phonological disorder, especially backing.
  • Bilingual and dialect considerations: Arabic has glottal and pharyngeal consonants as true phonemes. That does not make every glottal or pharyngeal production typical: judge each one against the intended target, its place and manner, and the context. Arabic-speaking children with cleft palate show compensations shaped by Arabic phonetics (Al-Awaji 2014), so English descriptions do not transfer directly.
  • How it’s identified: perceptual resonance and airflow assessment, oral examination, and referral to a cleft team.
  • Next: compare in the differential tool · see approaches in the Approach Finder
  • What it is: speech sound errors that result from reduced access to speech sounds.
  • Key features: there is no fixed profile; effects depend on severity and age of onset. Commonly reported patterns include final consonant deletion, voicing confusions, stops for fricatives and liquids, oral and nasal confusion, neutralised vowels, distorted resonance and slower transitions (ASHA).
  • Often confused with: phonological delay. Consider hearing status in every speech assessment, and arrange audiological assessment when history or findings suggest it.
  • Bilingual and dialect considerations: Effects may differ across languages, depending on which sounds are harder to hear in each and on the child’s exposure to each language.
  • How it’s identified: audiological assessment when indicated, alongside speech assessment.
  • Next: compare in the differential tool · see approaches in the Approach Finder

A note on persistence

Persistence describes continuing speech difficulties over time rather than a separate diagnostic category. It can occur across different SSD presentations, though the reasons differ: a persisting developmental SSD is not the same as continuing difficulty with a structural or hearing-related cause.

  • Terms: Shriberg’s system uses “Persistent Speech Disorder” for difficulties continuing after age 9, and “Speech Errors” for distortions, usually of sibilants and rhotics (Shriberg et al. 2010).
  • More than a few sounds: persistent SSD is not always a lisped /s/ or a distorted /r/. It can include ongoing phonological difficulties. In a UK population study, 3.6% of 8-year-olds had a persistent SSD even after common distortions were excluded (Wren et al. 2016).
  • Arabic: in a normative study of 60 Jordanian children aged 6;6 to 8;4, five of ten late-developing consonants had still not been acquired in their standard (Educated Spoken Arabic) form by the oldest children, although all ten were produced in acceptable colloquial forms (Amayreh 2003). Not yet using the standard form of these sounds at this age is not, on its own, a sign of disorder. This applies to those sounds in that population, not to Arabic acquisition in general.
  • Often confused with: accent, and late-acquired sounds still within the expected range.

Difference or disorder? Bilingual and dialect-aware assessment

No single rule separates difference from disorder in bilingual children. Accents and dialects are differences, not disorders (ASHA), and there is limited evidence that bilingualism itself slows speech development, although bilingual children may show different error patterns and cross-language transfer (Hambly et al. 2013). But an error in only one language can still be clinically significant, a disorder can look different in each language, and cross-language influence can affect shared sounds in both.

An international expert panel recommends assessing every language a child speaks, with more than one measure, at more than one point in time (McLeod, Verdon & IEPMCS 2017). Assessing one language alone can make transfer look like disorder (Margetson et al. 2023).

Questions that help weigh the evidence together:

  1. How does the pattern compare across languages? Look at what appears in both, what appears in one, and why. Neither alone settles the question.
  2. Could it be transfer? Check whether the sound or pattern exists in both phonetic inventories, and whether the error matches the structure of the other language.
  3. Is it expected for the child’s dialect and exposure? Compare with norms for the variety spoken at home, and consider how much exposure the child has had to each language.
  4. Is it developmentally expected? Use age norms for that sound in that language variety, where they exist.
  5. Is the pattern atypical in one language or across both? A pattern atypical in only one language may reflect transfer or limited exposure, but can still matter. Similar unexpected patterns across languages may strengthen concern, but do not establish a disorder on their own. Interpret them alongside language exposure, dialect, phonotactics, developmental expectations and consistency.

Language and dialect context decides which errors are clinically meaningful. Choosing a treatment approach then follows the same clinical reasoning as for any child. Planning how to deliver it is different: it should take account of the child’s language experience and proficiency (which can differ by skill and context), each language’s phonological system, likely cross-language generalisation and the family’s priorities.

A gap in the evidence: published Arabic norms include consonant acquisition data for particular dialects (for example, Jordanian Arabic: Amayreh & Dyson 1998). A recent review highlights the need for dialect-sensitive normative data to ensure valid assessment (Abdulkader 2026).

Printable: SSD Differential Comparison Chart

The profiles compared feature by feature, and what helps tell the most common confusions apart, on two A4 pages.

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References

  • Abdulkader, D. M. (2026). Instrumental and machine learning analysis approaches to speech sound disorder assessment in Arabic-speaking children: A review with narrative synthesis. Perspectives of the ASHA Special Interest Groups, 11(3), 1141–1159. Link
  • Al-Awaji, N. N. (2014). Speech production in Arabic speaking children with operated cleft palate. PhD thesis, University of Sheffield. Link
  • Amayreh, M. M. (2003). Completion of the consonant inventory of Arabic. JSLHR, 46(3), 517–529. Link
  • Amayreh, M. M., & Dyson, A. T. (1998). The acquisition of Arabic consonants. JSLHR, 41(3), 642–653. Link
  • American Speech-Language-Hearing Association. (2007). Childhood apraxia of speech [Technical report]. Link
  • American Speech-Language-Hearing Association. (n.d.). Speech sound disorders: Articulation and phonology [Practice Portal]. Link
  • American Speech-Language-Hearing Association. (n.d.). Speech characteristics: Selected populations. Link
  • Broomfield, J., & Dodd, B. (2004). The nature of referred subtypes of primary speech disability. Child Language Teaching and Therapy, 20(2), 135–151. Link
  • Chenausky, K. V., et al. (2020). Factor analysis of signs of childhood apraxia of speech. Journal of Communication Disorders, 87, 106033. Link
  • Dodd, B., McIntosh, B., Crosbie, S., & Holm, A. (2023). Diagnosing inconsistent phonological disorder: Quantitative and qualitative measures. Clinical Linguistics & Phonetics, 38(5), 453–476. Link
  • Eadie, P., et al. (2015). Speech sound disorder at 4 years: Prevalence, comorbidities, and predictors in a community cohort of children. Developmental Medicine & Child Neurology, 57(6), 578–584. Link
  • Hambly, H., Wren, Y., McLeod, S., & Roulstone, S. (2013). The influence of bilingualism on speech production: A systematic review. International Journal of Language & Communication Disorders, 48(1), 1–24. Link
  • Iuzzini-Seigel, J., et al. (2022). A tool for differential diagnosis of childhood apraxia of speech and dysarthria in children: A tutorial. LSHSS, 53(4), 926–946. Link
  • Margetson, K., McLeod, S., & Verdon, S. (2023). Cross-linguistic transfer and ambient phonology: Impact on diagnosis of speech sound disorders in a longitudinal bilingual case study. Journal of Monolingual and Bilingual Speech, 4(3), 311–339. Link
  • McLeod, S., Verdon, S., & International Expert Panel on Multilingual Children’s Speech. (2017). Tutorial: Speech assessment for multilingual children who do not speak the same language(s) as the speech-language pathologist. AJSLP, 26(3), 691–708. Link
  • Murray, E., McCabe, P., Heard, R., & Ballard, K. J. (2015). Differential diagnosis of children with suspected childhood apraxia of speech. JSLHR, 58(1), 43–60. Link
  • Murray, E., Iuzzini-Seigel, J., Maas, E., Terband, H., & Ballard, K. J. (2021). Differential diagnosis of childhood apraxia of speech compared to other speech sound disorders: A systematic review. AJSLP, 30(1), 279–300. Link
  • Shriberg, L. D., et al. (2010). Extensions to the Speech Disorders Classification System (SDCS). Clinical Linguistics & Phonetics, 24(10), 795–824. Link
  • Shriberg, L. D., et al. (2019). Estimates of the prevalence of motor speech disorders in children with idiopathic speech delay. Clinical Linguistics & Phonetics. Link
  • Ttofari Eecen, K., Eadie, P., Morgan, A. T., & Reilly, S. (2019). Validation of Dodd’s Model for Differential Diagnosis of childhood speech sound disorders: A longitudinal community cohort study. Developmental Medicine & Child Neurology, 61(6), 689–696. Link
  • Wren, Y., Roulstone, S., Miller, L. L., Emond, A., & Peters, T. (2016). The prevalence, characteristics, and risk factors of persistent speech disorder. JSLHR, 59, 647–673. Link