This article reports the results of an Economic and Social ResearchCouncil (ESRC) funded study which focuses on the differential academic achievement of different groups of pupils. The paper describes the findings on the size and extent of school effects across 3 years (1990, 1991, 1992) for different groups of pupils (classified by gender, eligibility for free school means [FSM], ethnic group and by prior attainment). Pupils' overall General Certificate of Secondary Education performance and their performance in selected subjects (English, English literature, French, history, mathematics and science) have been analysed using multilevel modelling, employing a total sample of 94 inner London secondary schools. A 'value added' approach is adopted, controlling for selected student background measures of prior attainment (at secondary transfer), gender, age, ethnicity and low income to provide statistical controls for differences between schools in the characteristics of their intakes. Differential school and departmental effects were identified for all pupil groups examined. However, the strongest evidence of differential effects was found for groups classified by prior attainment and ethnicity. Overall, the findings indicate that schools that appear to be more or less effective for a particular group of pupils, such as non-FSM pupils, are likely to be more or less effective for all pupils. However, in some schools, substantial differences between groups were identified. The implications of these findings for the debate about the publication, presentation and interpretation of schools' examination results and the extent to which the overall concepts of 'effective' or 'ineffective' schools can be applied, are discussed.