The research findings presented in this paper illustrate how the "value added" of schooling can be assessed empirically using cross-sectional data. Application of the regression-discontinuity approach within a multilevel framework produces both an estimate of the absolute effect of 1 year schooling and an estimate of the variation across schools of this effect. In the study reported here, the approach was applied to both a cross-sectional and a longitudinal dataset. The research findings indicate to what extent different results are produced when cross-sectional as opposed to longitudinal data are analysed. (Contains 2 notes, 3 tables and 4 figures.)