How far behind in number are socioeconomically disadvantaged pupils when they start school in England?

This paper examines the gap in number skills between socioeconomically disadvantaged and non-disadvantaged children in the first year of compulsory schooling in England. Past research mostly relies on statutory assessment data collected towards the end of the first year of school and does not show the attainment gap associated with socioeconomic disadvantage when pupils begin school, nor does it measure the size of the gap. The analysis presented here uses primary data from number assessments conducted in autumn 2023 and summer 2024 with 3018 pupils in 169 schools alongside National Pupil Database records to provide a new perspective on early number attainment. It finds that pupils defined as socioeconomically disadvantaged in their first year of school achieve number assessment scores 23.6% lower than other pupils. The effect size (g = 0.51) remains the same in follow-up assessments at the end of the school year. These findings have implications for government policy given stated commitments to increasing the number of pupils achieving a good level of development in statutory assessments at age 5.