Studies on advanced maternal age (35+) and children’s cognitive development report mixed evidence, possibly because they have analysed it in different time periods. We analysed trends in the association between advanced maternal age and standardized cognitive development at age 10/11 using three UK cohort studies: the 1958 NCDS (n=10969), the 1970 BCS (n=9362), and the 2001 MCS (n=11600). The results show that the association between advanced maternal age and children’s cognition went from negative in the 1958 and 1970 cohorts to positive in the 2001 cohort. These cross-cohort differences were explained by the fact that in the earlier cohorts advanced maternal age was associated with high parity, whereas in the 2001 cohort it was associated with advantaged family background. The time period and secular changes in the social meaning of having children at older ages can constitute important factors in determining the association between maternal age and cognitive ability.