Recent government initiatives encouraging diversity and the expansion of popular and successful schools have proved controversial, encouraging debate about the efficacy of faith schools. This paper takes a longitudinal approach drawing together Section 10 inspection reports and examination data to compare levels of academic attainment of Catholic and other schools in the post-16 phase of education. Pupils' levels of achievement vary according to the size and status of the sixth form. Tentative hypotheses to explain the somewhat equivocal findings are outlined and areas for further research suggested. (Contains 1 figure and 5 tables.)