Research emerging from the USA suggests that holding an incremental theory of intelligence (growth mindset) has a positive impact on academic success. However, limited empirical work has explored this relationship in a UK sample, and there has been a lack of research into the antecedents which might influence the development of certain intelligence beliefs. This study aimed to explore these gaps in the existing literature. Data was collected from 710 9-year-old pupils (UK Year 5). Participants completed attainment tests in Maths and English, and a questionnaire to assess their implicit theories of intelligence (mindset). Socio-demographic information--including gender, ethnicity, free school meal (FSM) status and special educational needs (SEN) status--was also collected. Results showed that pupils eligible for FSM or SEN endorsed more of an entity theory of intelligence than pupils not eligible for either. Analysis of the whole sample showed that attainment significantly correlated with implicit theories of intelligence, however, this relationship did not exist for children with FSM or SEN status. These findings help to elucidate the relationship between implicit theories of intelligence and attainment in the UK, but also suggest the importance of external support in potentially facilitating pupils' belief systems. Results are discussed in relation to avenues for targeted intervention.