Morphosyntax constitutes one of the most complex areas of language. It takes into account the structure of the word and that of the sentence, and its development allows one to establish adequately agreements both within the nominal phrase and in the rest of the sentence. Morphosyntax is particularly impaired in individuals with Down syndrome. To improve their morphosyntactic skills, an intervention programme was designed and carried out with a total of 20 Spanish-speaking children with Down syndrome; half of them composed the experimental group and the other half the control group. The results obtained show that the children in the experimental group improved more than the children in the control group in the areas of syntax, morphology and semantics, but not in pragmatics, where both groups improved to the same extent. Overall, the results obtained support the effectiveness of the programme implemented as a clinical and educational tool for intervention in individuals with Down syndrome. (Contains 2 tables.)