The study used learning environment variables in investigating changes occurring as students transfer from primary to secondary school, including the role of student sex and school size pathway as influencing factors in changes in learning environment perceptions. The My Class Inventory (MCI) and Questionnaire on Teacher Interaction (QTI) were used in two data-gathering stages, one in the penultimate month of primary schooling and the other in the fourth month of secondary schooling. The sample comprised 1500 students from 47 feeder primary schools and 16 linked secondary schools. The primary schools ranged from very small isolated country schools to larger city schools with hundreds of students. Five different school size transition pathways were defined for analysis: small-to-medium, medium-to-medium, small-to-large, medium-to-large and ‘within-school’ (involving schools with a K-10 structure, but with separate primary and secondary school sites within the same campus). Although the classroom climate in secondary schools was perceived more favourably than in primary schools (especially in terms of less friction and competitiveness), the quality of teacher-student interaction was perceived to deteriorate on most dimensions assessed by the QTI (e.g. a reduction in teachers' leadership, helping/friendly, understanding and student responsibility/freedom behaviours). But changes in environment perceptions across transition varied with student sex and school size pathway. For example, perceptions of class satisfaction across transition deteriorated for girls, but improved for the boys. The findings have implications for administrators and teachers, particularly those with a role within the ‘middle school’ years.