Recent research has claimed that American private high schools are more effective than public high schools. Two critical aspects of this research are at the center of this article: a) whether the short-term benefits of private schools which were found to exist persist over an extended period of time; b) whether these effects can be explained by differences in funding. In the Netherlands public and private education are equally funded. Longitudinal data on the educational attainment of the 1965-cohort during the whole of their secondary education were used to establish whether Dutch Catholic, Protestant and public secondary schools have differential effects on their pupils' educational achievement. The results of the study demonstrate the presence of a school sector effect in the Netherlands on the educational attainment of their pupils.