Children in the study participated in a comprehensive speech, language and literacy assessment five times during the two-year study, Dr McNeill said.
"Speech production, oral movements, vocabulary knowledge, listening comprehension, storytelling, grammatical skill, reading and spelling are among the areas of development being monitored.
"The study draws participants from Northland to Dunedin."
Dr McNeill has collected almost all the data for the project, with participants undergoing their final assessment in the next three months.
Initial analysis of the results showed participants were generally affected in their mouth movement, language and literacy development. More than 75 per cent of children in the study needed support in at least one area in addition to speech production.
More work was needed to enhance the literacy and educational achievement of children with the disorder, she said.
"Children with severe speech difficulty are usually referred for speech and language therapy support in the pre-school years. There's a lot we could be doing to facilitate early literacy development in this group, rather than waiting for difficulties to be recognised later on."
The best chance children affected by the disorder had to meet their communication and academic potential was to integrate speech therapy and educational support, Dr McNeill said.
About five per cent of New Zealand children were affected by some form of speech disorder.
Dr McNeill's project has received $300,000 from a Marsden Fund fast start research grant.
