Of all the developmental difficulties that may be present in childhood, language impairment is probably the most common. It is of vast importance to prevent cumulative negative consequences of these impairments. The present study evaluates the effects of a language and activity-based intervention programme on verbal and non-verbal performance and play behaviour in children diagnosed as having specific language impairment. Children with the same diagnosis and conventional early special education were used as controls. Verbal and non-verbal abilities and play behaviour were evaluated before and after intervention in both groups. The intervention sessions, aimed to develop the children's functional use of language and communication, were held in community day care centres. The sessions took place twice a week in groups of two to four children. The intervention had a positive influence on non-verbal performance and play behaviour. However, the intervention did not have any significant effect on language measurements. The results are discussed in the context of language development as a dynamic process with circular causation between different aspects of development. (Contains 2 tables, 3 figures, and 2 notes.)