A substantial body of research examines whether increasing the proportionality of an electoral system increases turnout, mostly based on cross-national comparisons. In this study, we offer two main contributions to the previous literature. First, we show that moving from a single-member district system to proportional representation in multi-member districts should, according to recent theories of elite mobilization, produce a contraction in the distribution of mobilizational effort across districts, and hence a contraction in the distribution of turnout rates. Second, we exploit a within-country panel dataset based on stable subnational geographic units before and after Norway's historic 1921 electoral reform in order to test various implications stemming from the contraction hypothesis. We find significant support for the predictions of the elite mobilization models. (122 words) Word count: 8,793 words (excluding title page and online appendix)