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Speech sound disorders are common in children, making up the majority of a Speech Pathologist’s caseload. Before going into disordered speech, let’s have a glimpse at what happens in typical speech development.

Typical speech development

Speech develops gradually. Over time, children develop their:

  • Intelligibility: they speak more clearly
  • Articulation (or Phonetics): they produce increasingly complex sounds with accuracy, by making the correct oral movements.
  • Phonology: they organise the sounds of their language in a way that resembles adult speech. This involves ‘storing’ the sound correctly in their mind, and ‘saying’ the sound correctly. The way each sound is ‘stored’ and the way it is ‘said’ will correspond correctly when mastered.

So, certain speech errors are a part of typical speech development. But by the time the child is about to start school, they should be 100% intelligible, and should be making few speech errors.

Speech Pathologists refer to milestone guides to determine what is expected, developmentally, in terms of a child’s intelligibility, articulation, and phonology.

See Speech for the Early 8, Middle 8 and late 8 consonant sounds that children acquire (i.e., articulation development) and examples of phonological processes (i.e., phonological development).

What is a speech sound disorder?

Children with speech sound disorders (SSD) differ in terms of: the kinds of speech errors they produce; the severity of their errors; the cause of the disorder; the age at which the disorder appeared, and their response to therapy.

As such, children with SSDs are a heterogenous group and the term “speech sound disorder” is only an umbrella term. In order to know which treatment is best suited to each child with a SSD, researchers have tried to classify SSDs using a variety of approaches. Classification approaches were based on: why the problem exists; how children with a SSD process speech, and what the SSD looks like (Waring & Knight, 2013).

Although there is no consensus on which classification system to use, recent research has supported the third approach, which involves the precise description and analysis of the child’s speech errors and linguistic abilities. This classification system has been shown to be useful in differentially diagnosing children and selecting appropriate intervention (Crosbie, S., Holm, A., & Dodd, B., 2005)

This approach identifies 5 subgroups of SSD (Dodd, 2014). A precise description of each subgroup is too technical for the purpose of general reading, so I will describe the 5 subgroups very simply:

Articulation disorder – a child with an articulation disorder will make consistent sound substitution or distortion errors. A lisp is a common example of an articulation disorder.

Phonological delay – this is where a child continues to speak using typical error patterns (i.e., phonological processes) that are no longer age-appropriate.

Consistent atypical phonological disorder – this is where a child makes phonological errors that do not occur in typical development. For example, it is typical for a young child to say “dou” instead of “go” (this process is called “fronting”) but it is not typical for a child to say “goor” instead of “door” (this atypical phonological process is called “backing”).

Inconsistent phonological disorder – a child with an inconsistent phonological disorder will say certain sounds in words inconsistently. For example, a child may say the /k/ sound in “car” differently, calling it “car”, “tar”, and “gar” on three separate occasions.

Childhood apraxia of speech (CAS) – this is a rare SSD that affects multiple areas of difficulty (i.e., phonetic and phonemic planning as well as oral motor coordination). Inconsistency is one of the key signs as well as difficulty in imitation and “groping” (i.e., searching for the correct oral position).

How common are Speech sound disorders (SSDs)?

SSDs are very common, making up more than 70% of a Speech Pathologist’s paediatric caseload (Mullen & Schooling, 2010). SSD’s begin in childhood and may persist into adulthood if not treated.

Of the subgroups, phonological delay is the most common, followed by consistent atypical phonological disorder, articulation disorder, and least common are: inconsistent phonological disorder, and childhood apraxia of speech (Dodd, 2014).

What causes speech sound disorders?

Most developmental speech sound disorders have no known origin.

We do not know what causes phonological disorder, articulation disorder or childhood apraxia of speech. These disorders often run in families, but this is not always the case.

We do have some information on risk factors. According to an Australian study, boys with a family history of speech impairment whose mother attained a low level of education were found to be 7.71 times more likely to have a speech impairment than a child without any of these factors (Campbell et al., 2003).

The SSDs with known origins include:

Structural disorders: e.g. cleft lip and/or palate, and other craniofacial anomalies. In these cases, the speech disorder is directly caused by the structural differences of the head or face.

Hearing loss: can be present at birth or it can be acquired. It can range in severity from mild to profound. It is common in certain genetic syndromes (e.g. Down Syndrome, Treacher Collins Syndrome) and it can occur after certain diseases (e.g. meningitis, chicken pox). It can also occur due to certain kinds of noise exposure. Children with recurrent ear infections are at risk of hearing loss. Hearing loss impacts on speech directly because it prevents the child from hearing and learning speech sounds accurately.

Genetic disorders: e.g., Fragile X. Genetic disorders impact on a child’s articulation, phonology, motor coordination, etc., in different ways.

Neuromotor disorders: e.g. Cerebral palsy. Cerebral palsy affects a person’s muscle control or coordination. As a result, many people with cerebral palsy have unclear speech (dysarthria) due to impaired muscle function.


A thorough speech assessment is necessary to correctly diagnose the SSD and to select the intervention that has been shown to be most effective for the specific deficits identified. Sometimes, there will be more than one choice and I will discuss this with you.

As there is a high co-occurrence of speech difficulties and language difficulties, assessment of both speech and language is recommended. An initial screening of speech and language can confirm whether language assessment should be conducted.

For more general information, see Assessment.