Two studies examined the relationship between precollegiate advanced/enriched educational experiences and adult accomplishments in science, technology, engineering, and mathematics (STEM). In Study 1, 1,467 13-year-olds were identified as mathematically talented on the basis of scores [greater than or equal to] 500 (top 0.5%) on the math section of the Scholastic Assessment Test; subsequently, their developmental trajectories were studied over 25 years. Particular attention was paid to high-level STEM accomplishments with low base rates in the general population (STEM PhDs, STEM publications, STEM tenure, STEM patents, and STEM occupations). Study 2 retrospectively profiled the adolescent advanced/enriched educational experiences of 714 top STEM graduate students (mean age = 25), and related these experiences to their STEM accomplishments up to age 35. In both longitudinal studies, those with notable STEM accomplishments manifested past histories involving a richer density of advanced precollegiate educational opportunities in STEM (a higher "STEM dose") than less highly achieving members of their respective cohorts. While both studies are quasi-experimental, they suggest that for mathematically talented and academically motivated young adolescents, STEM accomplishments are facilitated by a rich mix of precollegiate STEM educational opportunities that are designed to be intellectually challenging, even for students at precocious developmental levels. These opportunities appear to be uniformly important for both sexes. (Contains 6 tables, 3 figures and 1 footnote.)