Afasic estimates that more than a million children and young people are affected in the UK, potentially representing two children in an average classroom.
A Scottish Executive review of speech and language therapy for children suggested that around one in 200 children with a record of needs requires help and that another 8 per cent of children require periodic support.
Key issues highlighted in the review include:
* Waiting times for children to be assessed and receive therapy.
* A shortage of experienced therapists.
* High rates of absence - leaving children unsupported.
* Recruitment and retention "to meet the needs of children in an inclusive school system".
Linda Lascelles, Afasic's chief executive, said: "We hope that parents of children with speech and language disorders will help us with the survey by logging on to www.afasic.org.uksurvey and telling us their experiences."