I investigate the determinants of high school completion and college attendance, the likelihood of taking science, technology, engineering or math (STEM) courses in the first year of college and the probability of earning a degree in a STEM field. The focus is on women and minorities, who tend to be underrepresented in STEM fields. Tracking four cohorts of students throughout Florida, I find that large differences in math achievement across racial lines exist as early as elementary school and persist through high school. These achievement differences lead to higher drop-out rates in high school and a reduced probability of attending college for black students. However, conditional on immediately attending a four-year college after high school, black and Hispanic students are more likely than whites to take STEM courses during their first year in college. Increased exposure to Hispanic math and science teachers in middle and high school tends to increase the likelihood that Hispanic students take STEM courses during their first year in college, though pairing black students and black math/science teachers does not have the same positive effect. For all students, having high school math and science teachers with a degree in biology, chemistry or math (as opposed to education) is associated with a higher likelihood of taking STEM courses as college freshmen. When pre-college differences in income and math achievement are taken into account, black and Hispanic students are at least as likely as white students to successfully complete a STEM major. Racial/ethnic pairing of students and college instructors in first-year STEM courses does not increase the likelihood of majoring in a STEM field. In contrast to underrepresented minorities, women perform nearly as well as men on math achievement tests through high school and are more likely to finish high school and attend college than males. Among college students, however, women are less likely than men to take courses in the physical sciences in their first year and are less likely to earn a degree in physics or engineering, even after adjusting for pre-college test scores. Gender matching of students and math/science teachers in middle and high school tends to increase the likelihood that female college freshman will take at least one STEM course, However, conditional on first-year coursework, neither gender matching at the secondary or college levels appears to have any effect on the likelihood of completing a major in a STEM field.