This study investigates the counter-intuitive observation that older students tend to thrive better than younger students in online classes. We use a variety of measures to compare performance and attitudes of undergraduates and continuing adult professionals in separate but nearly identical class sections led by the same instructor at a US university during the same nine-month study period. Findings are consistent with theoretical predictions about differences in readiness of younger and older adults for self-directed learning experiences. Results also suggest that online educators should be proactive in stimulating younger students' participation in class discussions, and should find ways to evaluate explicitly the tacit learning that online discussion can foster. (Contains 7 figures, 9 tables and 3 notes.)