This thesis reports research undertaken during 1975 and 1976 in a co-educational multi-racial comprehensive school in London. The study aims to examine in what ways sex-class (in comparison with ethnicity and social class) structures relationships within the school. The author spent eight months in daily observation of five classes of 15 and 16 year-old pupils and their teachers. A framework is proposed for . understanding the development of gender identity (masculinity/ I femininity) which places the role of school in a wider context. Pupils' perceptions of teachers (in the abstract and of those who currently teach them); their understandings of the pupil role; their classroom behaviour; and their academic aspirations and achievement are examined in relation to their typifications of males and females and their own self-concepts as feminine/masculine. Relationships between these are neither as straightforward nor as consistently pro-male as previous research would indicate. Teachers* perceptions of male and female pupils are examined in the light of their own teaching values and of differential classroom behaviour Of Pupils- NO firm evidence of teacher bias towards/against one sex can be discerned. The status of female and male teachers is discussed. Males OCCUPY Most of the senior posts and in general enjoy higher status than females. In terms of those who teach, many school subjects are sexdifferentiated throughout the school, with Ifemalet subjects being more peripheral to the core curriculum. This sex-differentiation is closely paralleled in fifth year pupilst choice of subjects for study. The school was organised around pupils' sex-class. It is demonstrated that large areas of consensus regarding sex-class exist between pupils and teachers.