There is evidence that teacher judgements and assessments of primary school pupils can be systematically biased. This paper tests the proposal that stereotyping plays a part in creating these judgement inequalities and is instrumental in achievement variation according to income-level, gender, special educational needs status, ethnicity and spoken language. Using 2008 data for almost 5,000 pupils from the Millennium Cohort Study, it demonstrates biases in teachers’ average ratings of sample pupils’ reading and maths ‘ability and attainment’ which correspond to every one of these key characteristics. Findings go on to suggest that stereotypes according to each of income-level, gender, special educational needs status and ethnicity all play some part in forming these biases. The paper strengthens the evidence that stereotyping of pupils may contribute to assessment and thereby attainment inequalities, and concludes that an increased focus on tackling this process may lead to greater parity and a narrowing of gaps.