This paper focuses on whether education causally affects mental health at different ages. A positive association between education and mental health outcomes is established in the literature. However, whether this association is causal is under debate. This paper offers the most comprehensive answer to this question by using four measures of mental health as outcomes and analyses all policy changes that have been introduced to the school leaving age in the UK since World War II. The results show that the policies impacted on school leaving age in the expected manner, but no consistent effect on mental health is uncovered.