Financial literacy and cognitive capabilities are convincingly linked to the quality of financial decision-making, influencing savings, stock-picking, and avoidance of outright financial mistakes. Yet, there is little evidence that education intended to improve financial decision-making is successful. Using plausibly exogenous variation in exposure to state-mandated personal finance and mathematics training in high school, affecting millions of students, this paper answers the question "Can good financial behavior be taught in high school?" It can, though not via personal finance courses, which we find have no effect on financial outcomes. Instead, we find additional training in mathematics leads to greater financial market participation, more investment income, and better credit management, including less bankruptcy and fewer foreclosures.