A comprehensive, quantitative evaluation of an educational intervention program designed to reduce the attrition of minorities from the biological sciences was undertaken to ascertain whether such efforts adequately address the problem. Program participants had greater odds of persisting in basic math and science courses, and of graduating in biology, than did a comparison group, controlling for demographics and academic preparation. Undergraduate research greatly increased the odds of positive graduation outcomes. Program participants were also more likely to pursue graduate study than were university graduates overall. This evaluation demonstrates the value of such programs in increasing the representation of minorities in science.