Considerable evidence supports the association between language learning difficulties and behaviour in young children and this is likely to be particularly true of children raised in social disadvantage. Less is known about the way that different aspects of language, specifically pragmatics, interact with behaviour. This study examines the extent to which pragmatic language skills mediate the relationship between structural language skills and parent report of behaviour. It was carried out with 138 community ascertained monolingual English speaking primary school children raised in an area of marked social disadvantage. We found that pragmatic skills substantially mediate the relationship between language and behaviour in this group of children. Further analyses suggest that the mediational relationship holds for hyperactivity, peer related problems and overall impact score but not for emotional problems, conduct problems or pro-social behaviour. Pragmatic language skills underpin the relationship between language and behaviour in low SES (socio-economic status) children. This is specifically true for children exhibited signs of hyperactivity, peer problems and the perceived impact that these may have on the classroom teacher, parents and other children. These findings need to be replicated in both comparable and different populations but, if the relationship holds, it is likely to have considerable implications for the development of valid and effective interventions in this area. Furthermore they may lead to a more differentiated approach to behavioural difficulties.