Based on data from the 1980 and 1990 Household Surveys, we analyze educational expansion in Spain and estimate earnings equations for male family heads ; then rates of return to education in both years are compared. Furthermore we decompose the over-all average earnings differential over time to verify to what extent the magnitude of changes is due to variations in the characteristics of the working population during the 1980-1991 period, and how much of that differential is explained by differences in the pay structure.