Given that one important goal of physical education programs is to facilitate the adoption of physically active lifestyles, it is important to investigate ways that teachers can accomplish that goal. The purpose of this study was to investigate students' attitudes and motivation toward physical education with the goal of learning how to design class environments that will promote the adoption of active lifestyles. Specifically, we examined relationships between self-reported levels of physical activity, measures of health related fitness, attitudes toward physical education, perceived motivational climate, and engagement in physical education classes. Participants were 800 middle school students enrolled in physical education classes. Data sources included a cardiovascular fitness assessment (Hoosier endurance shuttle run, Safrit, 1995), skinfolds, self-reported levels of physical activity (Physical Activity Questionnaire for Children [PAQ-C], Kowalski, Crocker, & Faulkner, 1997), perceived competence (CY-PSPP; Whitehead, 1995), assessment of children's attitudes toward physical education (Subramaniam & Silverman, 2000), perceived motivational climate (Papaioannou, 1994), intrinsic motivation (Situation Motivation Scale, Guay, Vallerand, & Blanchard, 2000), and engagement in classes as measured by pedometers. Data were analyzed using correlational analyses. Self-reported levels of physical activity and the number of steps taken during physical education classes were correlated with health related fitness assessments. Children who reported higher levels of physical activity and those who took more steps during their physical education classes had higher levels of cardiovascular fitness and lower percent body fat as estimated by skinfolds. Learning climates that emphasized personal improvement and mastering tasks were associated with positive attitudes toward physical activity, higher levels of perceived competence, and higher levels of motivation. Levels of physical activity, perceived competence, and positive attitudes were positive predictors of intention to engage in physical activity in the future. The major findings of the study support several implications for teachers. Children who are currently engaged in activity perform better on measures of health related fitness and indicate that they intend to be active in the future. Positive attitudes toward physical activity are fostered in physical education classes where teachers emphasize learning and improvement rather than on outperforming other students. Creating climates where students can experience success when they exert effort is especially important for students who are inactive. It is also important to select tasks and activities that students find to be useful and enjoyable in order to foster positive attitudes and increase the likelihood that children will choose to be active.Keyword(s): research