This paper presents four case studies that are part of a larger study on admissions arrangements and impacts on school admissions for all local education authorities (LEAs) in England and Wales. It examines factors influencing the social composition of schools. A total of 23 LEAs completed interviews about their secondary school admissions arrangements. The four case study LEAs have significantly different market scenarios. Results show that recent national education policy has not been evenly implemented across LEAs. A combination of organizational, structural, and demographic factors have muted much of the potential impact of school reforms on school admissions. Normative patterns of school use have not been substantially affected by the market reforms or the administrative actions of LEAs. LEAs remain important arenas within which school choice operates because they define kinds of choice available to parents in their administrative boundaries. The Schools and Standards Framework Act has restored some power to LEAs to coordinate admissions across all admissions authorities within each LEA boundary. The case studies give an indication of the range of choice available to parents and show how this varies among LEAs. (Contains 19 references and 8 figures.) (SM)