Bilingual children were found to form a distinct subgroup within a large cohort of children with specific language-impairment (SLI) attending language units across England. They differed from the cohort as a whole, and from a language-matched monolingual 'control' group, on measures including language profile on entry to the unit, performance on standardised tests, emotional-behavioural state and probable future educational placement. This paper sets out the nature of these differences in more detail, and suggests some possible explanations for them.