The thing that most often brings parents to us for this particular profile isn't a single persistent error — it's the variability. "She said it perfectly yesterday, and now it's gone again." "He can say his own name clearly on Monday and three different ways on Tuesday." It's the unpredictability that wears families down, because it makes it almost impossible to know what to practise, what to expect, or whether progress is happening at all.
This article is about that particular picture — what speech pathologists call disordered or inconsistent speech sound production. It's distinct from a delay (where a child is on the typical developmental path, just behind schedule — see Delayed Speech Sounds at Six) and distinct from consistent atypical errors (where the errors are unusual but at least predictable — see Atypical Speech Sound Errors). What makes this profile different is that the errors themselves change, and that tells us something important about where the difficulty lies.
Let's break down what this means, how it's identified, and why it matters.
What Does "Disordered" Mean in This Context?
We want to be upfront about the language here. The word "disordered" can feel heavy, and we understand that. In clinical practice, we use this term specifically to describe the nature of the speech sound production — it tells us something important about how the child's speech system is working, and it guides us toward the right kind of help.
It doesn't mean there's something fundamentally "wrong" with your child. It means their brain is organising speech production in a way that makes it harder for them to produce sounds and words consistently, and they need a specific kind of support to build those skills.
How Is Disordered Speech Different from Delayed or Atypical Speech?
Professor Barbara Dodd's classification model for speech sound difficulties provides a helpful framework for understanding the differences. Dodd's model, which is widely used in Australia and internationally, identifies four main categories (Dodd, 2014):
| Category | What It Means | Key Feature |
|---|---|---|
| Articulation difficulty | A child can't produce a specific sound correctly due to motor or structural factors | The same sound is always affected in the same way |
| Phonological delay | A child uses typical developmental patterns but hasn't grown out of them at the expected age | Patterns are familiar and expected — just lingering |
| Consistent atypical errors | A child uses non-developmental patterns — errors that aren't part of the typical pathway | Errors are unusual but consistent — the same error happens every time |
| Inconsistent speech sound production | A child produces the same word differently on different occasions | Inconsistency is the defining feature |
Inconsistency as a Hallmark
Inconsistency is the single most important feature of disordered speech sound production, and it's what sets this profile apart from delayed and atypical patterns.
All children are slightly inconsistent with their speech sometimes — especially when they're learning new words or when they're tired. But children with a disordered profile show a level of inconsistency that goes well beyond what's typical. In assessment, speech pathologists measure this formally by asking a child to produce the same set of words multiple times and calculating the percentage of inconsistency.
Research suggests that when a child's production of the same words varies on more than 40 per cent of attempts, this signals a significant level of inconsistency that warrants a different therapy approach from what we'd use for delayed or atypical profiles (Dodd, 2014).
Some of the children I've worked with who sit in this inconsistent group are the ones whose families describe the "good day, bad day" pattern most vividly — and naming the inconsistency often comes as a relief, because it finally explains what they've been seeing. Why does inconsistency matter? Because it tells us something about how the child's brain is planning and programming the movements needed for speech. It suggests that the child doesn't have a stable "motor plan" for producing words — so each time they try to say a word, the brain is essentially working it out from scratch rather than drawing on an established pattern.
Childhood Apraxia of Speech: One Example
One well-known example of disordered speech sound production is childhood apraxia of speech (CAS). CAS is a motor speech difficulty where the brain has trouble planning and coordinating the precise, rapid movements of the tongue, lips, jaw, and palate needed for clear speech.
Children with CAS often show:
- Inconsistent errors — the same word comes out differently each time
- Difficulty with longer or more complex words — errors increase as words get longer
- Groping or searching movements — the child may visibly try to position their mouth before speaking
- Unusual prosody — their speech may sound flat, choppy, or have unusual stress patterns
- Limited consonant and vowel repertoire — they may use fewer different sounds than expected
- Difficulty imitating sounds or words on request
CAS is relatively uncommon, affecting an estimated 0.1 to 0.2 per cent of children, though exact prevalence figures are difficult to establish (Morgan & Webster, 2018). It's important to note that CAS is not a "one size fits all" diagnosis — children with CAS vary widely in severity and in how their speech presents.
In Australia, researchers at the University of Sydney have contributed significantly to our understanding of CAS. The work of Professor Patricia McCabe and her colleagues has been particularly influential — her team's systematic reviews and treatment research have shaped how Australian speech pathologists assess and treat children with CAS (Murray, McCabe & Ballard, 2014). Morgan and Webster's (2018) research has also helped establish diagnostic criteria for paediatricians and clinicians working with these children.
Both Speech Pathology Australia (SPA) and the American Speech-Language-Hearing Association (ASHA) have published position statements on CAS, emphasising that:
- Diagnosis should be made by a speech pathologist with expertise in motor speech difficulties
- CAS requires a specific, evidence-based intervention approach
- Therapy should be intensive and frequent
- CAS is a motor speech difficulty, not a language or cognitive difficulty (though these can co-occur)
It's also worth emphasising that CAS is not the only cause of inconsistent, disordered speech production. Some children show significant inconsistency without meeting the full criteria for CAS. Dodd's model captures this distinction — a child can have an inconsistent phonological profile without necessarily having CAS.
What Does Disordered Speech Look Like Day to Day?
For parents, disordered speech production can be particularly confusing because it's unpredictable. On a good day, your child might say a word clearly, and you think they've "got it" — only for them to produce it completely differently the next day. This inconsistency can make it hard to track progress and can be frustrating for both you and your child.
You might also notice:
- Your child is much harder to understand than other children their age
- They struggle more with longer or unfamiliar words
- They may become frustrated or give up when trying to say something difficult
- Their speech may seem to get worse when they're tired, excited, or under pressure
- Other people — teachers, grandparents, peers — have difficulty following what they're saying
If this sounds like your child, a comprehensive speech pathology assessment is an important first step.
A quick thought on hearing. Before diagnosing a speech sound disorder, it's important to be sure a child is hearing clearly. A lot of the sounds that get muddled — "s", "sh", "f" — sit right in the range that's most affected by things like glue ear. An audiologist visit is a straightforward first step.
Why Early, Accurate Identification Matters
Getting the right assessment and the right diagnosis makes a real difference for children with disordered speech. The therapy approaches that work for phonological delays (like minimal pairs) are not typically effective for disordered or inconsistent profiles. These children need approaches that focus on building stable motor plans for speech — and the earlier that work begins, the better the outcomes.
An accurate assessment also helps set realistic expectations. Disordered speech production often requires more frequent and intensive therapy than a straightforward delay, and progress can be slower — but with the right approach and consistent support, children do make meaningful gains.
If your child is very hard to understand and you've noticed that their speech errors seem to change from day to day, getting an accurate assessment is the most important first step. The right diagnosis leads to the right therapy — and the right therapy leads to real progress. Speaking Speech Pathology offers mobile speech pathology in your home across Brisbane's south side and Logan. get in touch with our team to find out more. Any actual clinical work — assessment, diagnosis, or therapy — happens through a proper consultation tailored to your child.
Ready for practical strategies? Read our companion article: Therapy for Childhood Apraxia of Speech and Disordered Speech: What Works in Brisbane
Alexandra Bouwmeester is a Senior Speech Pathologist (MSPA, CPSP) with over 14 years' experience assessing complex speech sound presentations. She uses Dodd's classification framework and stays current with Australian research on CAS and disordered speech production.
References
- Dodd, B. (2014). Differential Diagnosis and Treatment of Children with Speech Disorder (2nd ed.). Whurr Publishers.
- Morgan, A. T., & Webster, R. (2018). Aetiology of childhood apraxia of speech: A clinical practice update for paediatricians. Journal of Paediatrics and Child Health, 54(10), 1090–1095.
- Murray, E., McCabe, P., & Ballard, K. J. (2014). A systematic review of treatment outcomes for children with childhood apraxia of speech. American Journal of Speech-Language Pathology, 23(3), 486–504.
