This study investigates whether financial grants, allocated based on need rather than major, improves odds that economically vulnerable students will pursue science, technology, engineering, and/or mathematics (STEM) degrees. We implemented a privately-funded financial aid program in Wisconsin and conducted a randomized experiment of its effects for low and moderate-income students at 10 two-year and four-year colleges and universities. The additional financial support greatly increased the probability that students would persist in pursuing a STEM major and/or switch to a STEM major by the third year of school. However, it did not change the odds that students would remain enrolled. Implications for educational opportunity, practice, and policy are discussed.