Variations & Complications

Variations and complications

Below we describe the main aspects of stammering: developmental versus acquired, and overt versus covert – and set out some of the conditions which may co-exist with a stammer.

We also have information leaflets for parents, children, young people and adults which you can read and share with others. Download them here or order physical copies for free here.

Developmental & Acquired

The most common form of stammering is called 'developmental stammering'. It affects around one in 12 children, usually between the ages of 2 to 5 as they learn to speak. Stammering can also start in later childhood, but this is less common.

A far rarer form of stammering is known as 'acquired stammering' and usually occurs later in life. The main causes are a head injury, a stroke or conditions such as Parkinson’s disease. Other causes can be extreme emotional distress, medication or drugs.

Overt & Covert Stammering

Overt stammering is what you hear when people stammer. Most people who stammer will find ways to hide their stammer, to make their stammer less obvious. Someone who has a covert stammer, also known as an 'interiorised' or 'hidden' stammer, will appear not to stammer at all, or only stammer very occasionally. Typically, they will have:

●    high levels of fluency
●    high levels of avoidance, for example changing words or saying less
●    strong negative feelings about stammering.

Someone with an interiorised stammer will often:

●    hide the fact that they stammer
●    worry that people will find out they stammer
●    have few people in their life that know they stammer
●    feel ashamed of their ‘secret’ stammer 
●    search ahead in their mind for potentially difficult sounds
●    substitute feared words for others that are easier to say
●    use complex avoidance strategies to hide their stammer.

People whose stammering is more noticeable might also do these things; the difference is that someone with a covert stammer will appear largely fluent. While they may not be seen to stammer, emotionally and internally this will be something very much on their minds. It’s the emotional side of things that’s key here: the negative thoughts, feelings and constant avoidance to hide the stammer.

If you have a covert stammer, it can be hard for other people to understand how it makes you feel. People will reassure you that they never knew you stammered, so it can’t be that bad. This can leave you feeling like you're making an unnecessary fuss. 

In extreme cases you may have been so 'successful' in your hiding it, that in fact you are not believed for having a stammer at all. This can be very frustrating and painful, as it effectively denies you have a problem. Just because your stammer is hidden it is not less of a problem, it’s a different sort of problem.

If you have a covert stammer, then speech and language therapy can liberating. Speech and Language Therapists know how strong the feelings associated with hiding a stammer can be, and the impact it can have on your life.  


Someone who clutters has a very fast rate of speech, and talks in rapid bursts, making them hard to understand. This is closely related to stammering. People who clutter may:

  • leave off word endings
  • omit or distort sounds or syllables (“elephant” becomes “elphant”; “orange” becomes “orng”)
  • run their words together
  • use lots of fillers words, like 'as', 'um' or 'uh'
  • repeat or revise phrases, or words 
  • have difficulty organising thoughts or getting to the point
  • find it hard to slow down, even when asked
  • tend to interrupt.

Cluttering often exists alongside other speech differences, including stammering. Cluttering can also occur alongside attention deficit hyperactivity disorders (ADHD) or autistic spectrum disorder (ASD).

A person who clutters may be unaware of any difficulty, so a parent, manager or colleague may suggest that they get help because they find it hard to understand them.  

Speech and Language Therapists who specialise in stammering are also trained in supporting people who clutter, so if you have a clutter, or someone you know does, then contact the local NHS speech and language therapy service. Therapy will vary from person to person. Becoming more aware of when they aren’t being understood can help someone who clutters. They can then use strategies like pausing between phrases and sentences and over-articulating certain words to make themselves understood.


Cluttering (Stuttering Foundation of America) – useful guidelines for identifying cluttered speech and ideas for managing it, from the Stuttering Foundation of America. 

International Cluttering Association – a membership organisation (free to join) open to people who clutter and Speech and Language Therapists with lots of helpful information and advice.

First Online Cluttering Conference – from May 2010 is still accessible online.

Stammering & Down's Syndrome

Stammering is common in people with Down’s syndrome, who will often have other speech and language problems and hearing loss. This means someone with Down’s can be hard to understand. Down’s syndrome may also cause learning difficulties, which can affect the ability to understand and produce speech.

Someone with Down’s syndrome might:

  • repeat whole words or parts of words while trying to think of the next bit of the sentence ("it’s…it’s…it’s…big.")
  • have long pauses in the middle of the sentence when they can’t think of what to say next ("it’s a…ball.")
  • pause in unusual places in sentences, often followed by two or three words in a sudden rush that may be hard to understand ("I’m going swim…mint’morrow.")
  • stress the wrong word in a sentence or on the wrong part of the word
  • struggle to find the right speech sound to start the word off.

When talking with someone with Down’s syndrome, you can help by:

  • giving them plenty of time to speak and plan what they want to say
  • pause before responding or talking, and slow the conversation down
  • avoid finishing sentences or saying what you think they’re trying to say
  • if you haven’t understood what they said, ask them to repeat it. It’s best to be honest
  • avoid long or complicated sentences
  • give positive encouragement for the message rather than the style of delivery
  • use gestures to illustrate your conversation. 

Let them know you value what they are saying and want to hear them.

Useful sources of support

The Down’s Syndrome Association

For Families and Carers: Communication series – practical tips and activities from the Down's Syndrome Association, for supporting children and young people to develop their communication skills. 


Exploring Fluency in Down's Syndrome – a discussion of speech dysfluencies for professionals and parents by Monica Bray (2016).

Tourette’s Syndrome

Tourette’s Syndrome (TS) is thought to affect about one per cent of the population, affecting all races and ethnic groups equally. It typically starts around the age of 6, with very few children developing TS beyond the age of 13. In up to 70% of children with TS, the tics will significantly reduce or diminish by late adolescence.  

Tourette’s Syndrome and stammering share many characteristics. They are both neurological conditions – that is the cause for both lies within the brain. Both have a strong genetic component and both affect more boys than girls.  

The main signs of TS are involuntary sounds and movements. This includes unintentional repeated movements, such as shoulder shrugs, eye-blinking or head twitches and repeated sounds such a throat clearing, sniffing, making a specific noise or repeating words or phrases.

Saying rude words or swearing is probably the best-known sign of TS, but this only affects a small number of children.

Like stammering, no two people with TS display precisely the same tic characteristics.

TS can be managed with medication, behavioural management and counselling support. Sometimes the vocal tics of children with TS may resemble stammering behaviours. If you think your child may be stammering and would like support with this, ask your GP or refer yourself to your local NHS Speech and Language Therapist. If possible, see someone who specialises in working with children who stammer.

Sources of Support and Information

Tourette's Action (Helpline: 0300 777 8427)

Tic Disorders: A Guide for Parents and Professionals a book by Uttom Chowdhury and Tara Murphy (2016), Jessica Kingsley Publishers.

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