This paper investigates whether mothers' participation in post-compulsory education impacts on children's relative inequalities across four developmental outcomes. The empirical analysis uses information from children born in 1958 in Britain. Mothers of the 1958 British cohort were affected by the 1947 school leaving age reform, which increased the age of compulsory schooling from 14 to 15 years. We selected the first-born cohort members whose mothers were born in 1933 and 1934 and whose mothers completed compulsory schooling only. We found that the additional year of maternal schooling was significantly associated with relative improvements in mathematics attainment for their children, but no significant differences for reading or behavioural outcomes. The impact on mathematics was mainly for boys. These results suggest wider dispersion in mathematics attainment between sons whose mothers benefited from the additional year of schooling in 1947 and those whose mothers did not. (Contains 6 tables and 6 notes.)