Meeting the current demand for STEM graduates requires significantly increasing the number of students majoring in STEM fields. One program designed to increase the number of STEM majors is Project Lead The Way (PLTW). Using statewide data from Indiana, this research examined the effects of PLTW participation in high school on the likelihood of majoring in STEM during college. Propensity score matching and weighting were used to provide a rigorous evaluation of PLTW that would allow causal inferences to be made about program effectiveness. Results indicated that PLTW participation significantly increased the likelihood that students who attend college will major in a STEM discipline. The results also indicated a dosage effect for PLTW participation. Specifically, completing one PLTW course increased the likelihood of majoring in STEM by 0.16, and completing two PLTW courses increased the likelihood of majoring in STEM by 0.27. Completing three or more PLTW courses increased the likelihood of majoring in STEM by 0.38. Tests of the conditional independence assumption also revealed that it was unlikely that these results were the product of external, unmeasured variables. Thus, it appears likely that PLTW participation has a direct, causal effect on majoring in a STEM discipline during college.