The rise in educational enrolment is often cited as a possible cause of the trend to later childbearing in developed societies but direct evidence of its contribution to the aggregate change in fertility tempo is scarce. We show that rising enrolment, resulting in later ages at the end of education, accounts for a substantial part of the upward shift in the mean age at first birth in the 1980s and 1990s in Britain and in France. The postponement of first birth over that period has two components: a longer average period of enrolment and a post-enrolment component that is also related to educational level. The relationship between rising educational participation and the move to later fertility timing is almost certainly causal. Our findings therefore suggest that fertility tempo change is rooted in macro-economic and structural forces rather than in the cultural domain.