This brief summarizes the results of a gender impact evaluation study, entitled preventing child marriage : lessons from World Bank Group (WBG) gender impact evaluations (IEs). Child marriage is closely linked to poverty and girls’ educational opportunities. Across 18 of the 20 countries with the highest prevalence of child marriage, girls with no education are up to six times more likely to marry than girls with a secondary education. Girls living in poorer households are almost twice as likely to marry before the age of 18, compared with girls in higher-income households. Drawing on results from seven IEs supported by the WBG, this brief highlights lessons learned about what works to delay age of marriage and reduce child marriage. Effective programs will ultimately increase girls’ educational attainment, increase girls’ value and opportunities in society, and reduce poverty. Promising interventions are beginning to address the drivers of child marriage. However, more rigorous and long-term IEs are needed to better understand intervention components and delivery mechanisms that are effective in preventing child marriage.