This paper investigates whether long-term outcomes are affected by the duration of maternity leave, i.e. by the time mothers spend at home with their new-born before returning to work. It specifically examines the association between the length of parental leave and children's later PISA test scores at age 15. While they found no significant overall impact of extended parental leave mandate on young people's standardised test scores on the PISA at age 15, the subgroup of boys of highly educated mothers benefited from their mothers' extended parental leave. In contrast, boys of low educated mothers were harmed by it.