Background: Previous research findings from Project Active Teen demonstrated the effectiveness of high school conceptual physical education (CPE) in promoting active lifestyles. Method: This study followed Project Active Teen participants 20 years after graduation from high school and 24 years after taking a CPE class. Physical activity behaviors were assessed using the same procedures as previous Project Active Teen studies. Activity patterns were compared with patterns while in high school and shortly after high school graduation. Activity patterns were also compared with a national sample of age-equivalent adults. Results: Twenty years after high school graduation, former CPE students were less likely to be inactive and more likely to be moderately active than when in high school and were less likely to be inactive and more likely to be moderately active than national sample age-equivalent peers. They were typically not more vigorously physically active than comparison groups. Conclusion: Results support the long-term effectiveness of CPE in reducing inactive behavior and promoting moderate physical activity later in life.