We study the effect of the electoral system (single-ballot vs runoff) on the quality of politicians, measured by the average educational attainment, at the local level in Italy over the period 1994–2017. By exploiting the discontinuous voting rule shift nearby the 15,000 population cut-off, we have implemented a RDD and found that the change in the electoral scheme leads to an overall downward variation in the educational attainment of local politicians by about 2 % compared to years of schooling of politicians in municipalities just below the cut-off. Findings are similar when we separately focus on the educational attainment of mayors and councilors, and when we use alternative measures of quality of politicians related both to the previous occupation and to previous political experience. However, different confounding policies related to the voting scheme change at the cut-off. We show that the negative effect is not directly related to the way politicians are elected (runoff vs single-ballot scheme) but to the number of lists supporting the mayoral candidates: in municipalities below 15,000 inhabitants candidates running for mayor are supported only by one single list, whereas above the cut-off mayoral candidates might be supported by more lists. Overall, we speculate that the negative impact produced by the treatment on the educational attainment of local politicians is explained by the different selection process of candidates adopted by political parties, rather than by voters’ preferences toward low-skilled politicians.