Description: Educational researchers have long grappled with the problem of untangling the relative importance of school, class and group effects, often finding it easier to gather data and identify processes at the school level rather than at the detailed level of the classroom or teaching group. School composition research is no exception. Even qualitative work in this area, such as that of one of the authors, has tended to focus on the school level, identifying compositional effects on school organisation and processes, on peer relations, and on pedagogies adopted across the school. Effects of class or group composition, and their interaction with school level effects, represent another more sophisticated level of investigation . However, we also know from research on ability grouping that it matters which set a pupil is in, both in terms of educational outcome and attitude, self esteem etc. But studies of ability grouping have tended not to focus on school context or student composition. In the Hampshire Research in Primary Schools project, we attempt to bring these two strands of enquiry together to provide a fuller picture of compositional effects. We do this both quantitatively and qualitatively. Quantitatively, we look at outcome and progress data for Yr 4 students in primary schools of different composition and with different grouping practices. Qualitatively, we select two children, in two classes in each of12 schools, all of similar social class background and prior attainment. Some of these pupils are in mixed ability classes for all subjects. Others are set or grouped within classes. In each school, we follow the matched pairs to their lessons in different subjects and different sets, as well as observing their playground interactions and talking to them, their friends and their teachers. Thus we can examine not only the different school-level processes, pedagogical approaches, and peer groups that the children experience, but also the specific impact of setting and grouping practices and their interaction with year level student composition and their interaction with school policies and curriculum provision. We will address the following questions:- Are grouping strategies influenced by school composition?- What are the impacts of groupings on pupils in terms of their classroom experiences, curriculum provision, interest and engagement, and peer relations?- Do peer relations aid learning processes or militate against them? Methodology: This is a qualitative study with quantitative input Conclusions: To be reported. However, it is likely that groping practices will mediate compositional effects