What citizens know about the political system and its actors is a central factor when it comes to political engagement. Analyzing data from the Comparative Study of Electoral Systems, including recent data from the fourth wave, which, for the first time, includes a set of common political knowledge questions, this paper uses Bayesian multilevel models to investigate how and why political knowledge varies among citizens. The results confirm that education explains what citizens know about politics, but also show that the effect of education varies with the country’s degree of economic inequality and the proportionality of the electoral system.