A high rate of youth unemployment is one of the toughest problems facing African countries and which threatens the attainment of the sustainable development goals. Entrepreneurship education interventions are thought to be helpful in creating entrepreneurs whose activity will ultimately help to reduce the burden of youth unemployment. However, do such interventions work consistently in the long term? Drawing upon the theory of planned behaviour and a new typology of impacts, we tackle this question in the context of a long-standing entrepreneurship education intervention in Nigeria. We use pooled cross-sectional data from a sample of over 12,000 Nigerian undergraduates and apply an instrumental variable approach in a difference-in-differences (DiD) regression framework to obtain intention-to-treat estimates, thereby avoiding overoptimistic estimates of impact. The results show that despite a strong positive instantaneous impact, the longer the policy has been in place, the weaker its effect. In real life, it means that the policy is unable to continue to generate the desired impact of increased interest in entrepreneurship among repeated student cohorts, all else being equal. We suggest ways to overcome the inconsistency of impact and drive long-term social change; these include differentiating entrepreneurship curriculum to match students’ pre-course profiles. Overall, our study provides the first long-term impact evaluation of an entrepreneurship education intervention in a developing country context. Thus, we advance the policy debate on how to design and implement effective entrepreneurship education interventions that can foster youth entrepreneurship and employment.