Longitudinal studies can provide individual histories of educational attainment and are becoming widely used in educational research. Two national longitudinal studies, the National Child Development Study (NCDS) and the British Cohort Study of 1970 (BCS70), are used here to investigate changing trends in the educational attainment of children in the UK over time. Multilevel modelling is used to examine variation between different social groups in attainment in mathematics and reading and to examine educational progress during secondary education; the results of these analyses are compared for the two different cohorts. In both cohorts, the main source of variation in achievement is due to differences in social background; differences between regions and local education authorities are found to be negligible. Changes in the mathematics and reading attainment of the different social groups between the cohorts reflect recognized trends in educational attainment and highlight some trends not previously reported.