The validity of interval and time sampling methods of measuring student engaged time was investigated in a study estimating the actual time students spent engaged in relevant motor performance in physical education classes. Two versions of the interval Academic Learning Time in Physical Education (ALT-PE) instrument and an equivalent time sampling method were compared with actual time students spent in motor performance. Subjects were 36 college students enrolled in six different physical education classes: aerobic dance, badminton, basketball, fencing, karate, and volleyball. All instruction was videotaped so that each student could be coded throughout the class. The actual student engaged time and engaged time as estimated by the time sampling instrument were significantly lower than the time as estimated with the two ALT-PE instruments. In addition, a class type by coding instrument interaction occurred indicating that the difference was present for all classes except aerobic dance, where activity is continuous. This result suggests that the popularity of the ALT-PE instruments should be reexamined. (Author/GDC)