This article is based upon a secondary analysis of three successive cohorts of the Youth Cohort Study of England and Wales and examines the effects of social class and ethnicity on gender differences in General Certificate of Secondary Education (GCSE) attainment for those who left school in 1997, 1999 and 2001 respectively. The article shows that both social class and ethnicity exert a far greater influence on the GCSE performance of boys and girls than gender. Within this it assesses whether there is an interaction effect between gender and social class and also gender and ethnicity in terms of their impact on educational attainment. The article shows that, across all three cohorts, there is no evidence of any systematic variation in the size of the gender differences in educational attainment that exist across either social class or ethnic groups. Simply in terms of the effects of social class, ethnicity and gender on educational attainment, therefore, it is argued that these can actually be understood in terms of a simple "additive model". The implications of this for initiatives aimed at addressing gender differences in educational attainment are considered briefly in the conclusion. (Contains tables and 2 notes.)