The purpose of this study was to compare physical education and recess physical activity levels of elementary students with mental retardation and students without disabilities possessing either high or low cardiorespiratory fitness. The System for Observing Fitness Instruction Time (SOFIT) instrument (validated for use with students with mental retardation) was used to determine physical activity level. The theoretical framework for this study was social cognitive theory. Participants were 19 students possessing high cardiorespiratory fitness, 19 students possessing low cardiorespiratory fitness, and 8 students with mental retardation in grades three, four, and five. Participants were observed and videotaped during physical education (5 to 8 sessions) for a duration of at least 30 minutes and during recess (2 to 5 sessions) for a duration of at least 10 minutes. A 3 (group) X 2 (physical activity setting) factorial design was employed. ANOVAs were used to determine significant differences among the three groups during physical education and recess. A significant difference was obtained across settings for low physical activity and moderate to vigorous physical activity (MVPA), illustrating that participants were more active during recess (66%) than physical education (24%). Results also showed that groups were significantly different on LPA, F (2, 43)=12.85, p=.0001, and MVPA, F (2, 43)=12.81, p=.0001 during physical education. During physical education the participants possessing high cardiorespiratory fitness were more active (28%) at the MVPA intensity than participants possessing low cardiorespiratory fitness (21%) and participants with mental retardation (23%). These findings suggest that students with and without disabilities are more active during recess than physical education. Further, nondisabled students possessing low cardiorespiratory fitness are likely to have lower physical activity levels than nondisabled students possessing high cardiorespiratory fitness. Students with mental retardation have similar physical activity levels when compared to students possessing low cardiorespiratory fitness.Keyword(s): adapted physical activity, measurement/evaluation, physical activity