High school students have high ambitions but do not always make choices that maximize their likelihood of educational success. This was the motivation for investigating the relationships between high school sexual behavior and two important milestones in academic attainment: earning a high school diploma and enrolling in distinct postsecondary programs. The analysis of data from 7,915 participants in the National Education Longitudinal Study of 1988-94 presented here indicated that the timing of sexual initiation, the nonuse of contraceptives, and parenthood all predict female and male students' academic attainment. Furthermore, sexual behavior has more ramifications as attainment milestones become more competitive. These findings point to the importance of considering how students' choices across multiple life domains influence academic attainment, an important predictor of socioeconomic opportunity in adulthood. (Contains 2 tables and 10 notes.)