Graduate and doctoral schools around the world struggle to shorten the long time to degree and to prevent high dropout rates. While most of previous research studied individual determinants of PhD completion, we analyze the impact of two structural reforms of the doctoral program on thesis completion at a selective European graduate school. Exploiting a unique PhD dataset covering 30 entry cohorts, we identify reform effects on PhD outcomes using an interrupted time-series regression design. We find that the first reform improved timely completion rates by between 10 and 15 percentage points (according to the specific outcome), whereas the second reform increased completion rates by between 9 and 20 percentage points. Additionally, each reform reduced dropout rates by 7 percentage points. The results are robust to various sensitivity checks. At the end, we discuss lessons learned for those in charge of graduate schools and/or PhD programs.