This paper investigates the role of intergenerational social mobility in completed fertility of women born between 1948 and 1972 in Poland. It examines the hypothesis of acculturation, which implies that fertility of the mobiles will be in between that seen in their parents’ (origin) and their new (destination) stratum. Using a 2013 large-scale survey I employ diagonal mobility models and explore the interplay between completed fertility and woman’s education, her parents’ education, educational mobility and the sibship size. I compare birth cohorts whose reproductive careers took place before and after the collapse of communism. The results suggest that educational mobility was very stable over time, oscillating around 70%; nine out of ten mobiles moved up. Fertility exhibited a strictly negative educational gradient; fertility of the upward and downward movers tended to be lower and higher, respectively, than that of the non-movers. Except for daughters of at least one highly educated parent, the destination stratum played a much more important role in the achieved family size than the origin.