Studying the effectiveness of remediation courses in higher education has attracted a lot of interest from educational researchers and practitioners. Remediation is associated with significant economic and social costs while the results are usually dubious. In this paper, we applied a widely used method called Regression Discontinuity Design to measure the effectiveness of mathematical remediation courses of the Budapest University of Technology and Economics. Our large-scale study is based on data of 20,000 undergraduate students enrolled between 2010 and 2018 spanning 16 semesters. We study both the direct and longer term effect of remediation and find that it has small but statistically significant positive effect on further academic achievement.