Interpersonal discussion is considered to be one of the most influential sources of opinion formation and behaviour. Yet, an unresolved puzzle remains within the literature: while some studies show that discussion with not like-minded citizens depresses political participation, other studies, on the contrary, indicate that the same type of interpersonal discussion can foster political engagement. In this study, we address this unresolved democratic dilemma for the first time in a context of direct democracy, by focussing on the campaign leading to the 2016 Italian constitutional referendum. Specifically, we pay particular attention to the interaction between network diversity, ambivalence, and political knowledge. The findings show that frequent interactions with not like-minded citizens increase turnout. The results based on regression models and structural equation modelling indicate that this positive effect is channelled mainly through political learning, since network diversity increases factual knowledge about the constitutional reform, which in turn is associated with an increase in turnout. We do not find a significant effect of network diversity on ambivalence, as predicted by previous studies. These findings have important implications for deliberative theories and campaign strategies.