In January 2016, Tanzania implemented a fee-free secondary school reform. Using variation in district and cohort exposure to the reform, we employ a difference-in-differences strategy to estimate the short-term impacts of the reform. Despite a relatively small drop in user costs, the reform substantially increased enrolment into secondary education. While these enrolment effects were predominantly driven by an increasein public school enrolment, there was also a delayed positive effect on private school enrolment. Districts most exposed to the reform experienced a significant drop in exam scores relative to less-exposed districts, which cannot be explained by academic abilities of new students. These findings are in line with a theoretical school choice model, where fee elimination loosens enrolment constraints, and increased enrolment harms the quality of public education.