This paper examines the development of the impact of family background on young people’s political engagement during adolescence and early adulthood in order to test a number of hypotheses derived from the impressionable years and family socialization perspectives. The study analyses data of the British Household Panel Study and Understanding Society to assess these hypotheses. Political interest and voting intentions are used as outcomes of political engagement. The study finds parental education to have no effect on initial levels of these outcomes at age 11 but to be positively related to the change in these outcomes between ages 11 and 15. This indicates that the effect of parental education becomes stronger over time and that social disparities in political engagement are widening significantly during early adolescence. In contrast, parental political engagement is positively related to initial levels of voting intentions at age 11 but not related to the change in voting intentions between ages 11 and 15, which supports the hypothesis drawn from the family socialization perspective. Neither parental education nor parental political engagement are related to post-16 changes in political engagement. These results point to early adolescence as a crucial period for the manifestation of social inequalities in political engagement. They provisionally suggest that the influence of parental education runs through educational conditions in lower secondary and that these conditions could play an important role in amplifying the said inequalities.