Though the impact of deliberative polling on attitude change has received ample attention in the literature, micro models of attitude change before, during, and after deliberation are understudied. The relative strength of three competing views of the way attitudes change—the heuristics, systematic, and deliberative models—is assessed, using the quasi-experimental data of the EuroPolis deliberative project and comparing a group of people who participated in the deliberative poll with a control group. The results are: (1) in line with the systematic model, predispositions play a larger role than in the heuristics or deliberative models; (2) predispositions play a different role for participants and nonparticipants; (3) predispositions shape attitude formation in different ways depending on the issue at hand. On some issues the beliefs of participants change as a consequence of deliberation and become more complex and nuanced than before. This is, however, not the case for immigration issues where deliberation seems to strengthen predispositions.