This paper provides further evidence on the positive impact of schooling on within-groups wage dispersion in Portugal, using data on male workers from the 2001 wave of the European Community Household Panel. The issue of schooling endogeneity is taken into account by using the newest available instrumental-variable technique for quantile regression, i.e. the control-function estimator due to Lee (forthcoming, 2007). The findings are compared with earlier results based on different techniques, i.e. the instrumental-variable estimator due to Arias, Hallock and Sosa-Escudero (2001) and the standard exogeneity-based estimator due to Koenker and Bassett (1978).