Background. Children with Attention Deficit Hyperactivity Disorder (ADHD) have been found to achieve lower grades at school than their peers. Does this extend to pupils who are apparently exceptionally inattentive, hyperactive or impulsive, but have not been diagnosed as having ADHD? Aims. This study determined the proportion of children who were assessed by their teachers as exceptionally inattentive, hyperactive or impulsive in the classroom. The relationships between these traits, achievement and progress were examined. Sample,. The participants comprised 4148 children from a nationally representative sample of schools in England. Methods. Reading and mathematics achievement of the participants was assessed at the start and end of the reception year, and in year 2. Behaviour was assessed at the end of reception using a rating scale based on the diagnostic criteria for ADHD (American Psychiatric Association, 1994). Results. The proportion of children with exceptional scores on the behaviour rating scale was reported. The reading and mathematics attainment and value-added of children with high scores on the behaviour rating scale were found to be educationally and statistically significantly lower than children with zero scores. Conclusions. The achievement of children with high scores on the behaviour rating scale replicated previous studies which investigated the achievement of children with ADHD. The behaviour rating scale could be a useful tool for raising the awareness of teachers to young children with severe behavioural problems of inattention, hyperactivity and impulsivity who have not been diagnosed as having ADHD but may nevertheless be at risk of similar outcomes.