Private schooling in Uganda

Private Secondary Education in Uganda: Implications for Planning
by W. James Jacob, Donald B. Holsinger & Christopher B Mugimu
Teacher's College Record— 2008

Results: Private schools in Uganda appear to be attractive, low-cost alternatives to government secondary schools. Per-pupil spending is significantly related to learning achievement, regardless of whether a student attends a private or government school. Thus, if higher performance is the desired ultimate student outcome, additional spending will be required. For their per-pupil cost, this article shows that private schools produce good learning gains—better, in fact, on a dollar basis, than government schools.

I can't see how they control for self-selection (better students go to private schools) because I have to pay for the article...