The superior performance of girls, especially in terms of GCSE examinations, continues to attract attention. Much of the debate to date, however, has focused on absolute differences in attainment rather than differences in pupil progress. Furthermore, the role of the school in contributing to the differential progress of the two sexes has been little explored in previous research on school effectiveness which has been largely gender-blind. The research reported here tracks the progress of over 450,000 pupils in almost 2,700 English mixed secondary schools from Key Stage 3 to GCSE.First, a typology for understanding gender-related school effects, which relates schools' overall 'effectiveness' to the relative progress of the two sexes in individual schools, is developed. Then the extent to which schools are distributed across the different cells of the typology is considered. The analysis confirms expectations that there are a very considerable number of schools where girls have been making greater progress than boys between KS3 and GCSE and also that there are hardly any where boys' progress has been superior to that of girls. An unexpected finding, however, was the discovery that in almost half the schools in the country the progress of the two sexes was broadly equal. Furthermore, in a substantial minority of schools raising the overall levels of performance of both sexes may well be a more pressing priority than reducing the gender gap. The implications of the framework for the development of strategies designed to reduce the 'gender gap' are then considered. Figure 1b: GCSE point score v. KS3 average levels for two schools with different levels of effectiveness Figure 1a: GCSE point score v. KS3 average level--national lines for boys and girls.