While there is global interest in decentralizing school governance to enhance educational improvement and access, New Zealand moved two decades ago toward a self-managing model for schools, including giving many schools the ability to impose geographic admissions schemes when oversubscribed. This offers a useful test case for studying how schools use autonomy in more competitive environments, and the impact on access for disadvantaged students. Using geo-spatial analyses, we examine the process by which schools draw their own attendance boundaries relative to the demographic distribution of different communities. The evidence indicates that many more affluent schools create zones that, individually and in the aggregate, limit access to more desirable schools for children from disadvantaged backgrounds. The patterns suggest that schools may do this in order to protect or enhance their market positions.