This paper addressed relations between language, social communication and behaviour, and their trajectories, in a sample of 9–11-year-olds (n =91) who had been referred to clinical services with concerns about language as pre-schoolers. Children were first assessed at 2½–4 years, and again 18 months later. Results revealed increasing differentiation of profiles across time. By 9–11 years, 11% of the sample had social communication deficits, 27% language impairment, 20% both, and 42% neither. The size of group differences on key language and social communication measures was striking (2–3 standard deviations). Social communication deficits included autistic mannerisms and were associated with social, emotional and behavioural difficulties (SEBDs); in contrast, language impairment was associated with hyperactivity only. Children with both language and social communication problems had the most severe difficulties on all measures. These distinct school-age profiles emerged gradually. Investigation of developmental trajectories revealed that the three impaired groups did not differ significantly on language or SEBD measures when the children were first seen. Only low performance on the Early Sociocognitive Battery, a new measure of social responsiveness, joint attention and symbolic understanding, differentiated the children with and without social communication problems at 9–11 years. These findings suggest that some children who first present with language delay or difficulties have undetected Autism Spectrum Disorders which may or may not be accompanied by language impairment in the longer term. This new evidence of developmental trajectories starting in the preschool years throws further light on the nature of social communication and language problems in school-age children, relations between language impairment and SEBDs, and on the nature of early language development.