The academic advantage associated with having a university-educated parent may be intrinsic to that condition or depend on the proportion of university-educated parents in a society. If the latter, the expansion at university level will bring about a decrease in the average performance of children from university-educated families. I capitalize on the research opportunity that offers a late-expansion case such as Spain and assess how the academic achievement of students coming from university-educated families has evolved across the successive PISA waves. I document a strong decline that is partially explained by the increasing number of university-educated parents (particularly fathers) without a highly-skilled job. Furthermore, as the expansion of university causes the increase of hypogamous university-educated families where girls have an advantage, I test whether the decline in academic achievement is different for boys and girls. I observe no decline in academic achievement for girls coming from hypogamous university-educated families.