In this article, we have studied the effect of student social background, classroom social context, classroom organisation, and teacher behaviours on mathematics achievement and attainment in English and Welsh primary schools. Data were collected over 2 years as part of a programme evaluation, for which we observed 138 teachers and tested and collected background data on over 3,000 students. Results were analysed using multilevel modeling, and point to the importance of student background and teacher behaviours to achievement and attainment. The implications of these findings are explored. (Contains 10 tables.)