The main goal of the current study was to compare physical activity levels during swimming and nonswimming elementary physical education classes. We conducted a preliminary study and found that the System for Observing Fitness Instruction Time (SOFIT) could be used to register physical activity engagement levels in swimming classes. Thirty-nine classes, involving 8- to 12-year olds, participated in one swimming and one nonswimming physical education class. Classes were videotaped and physical activity levels for 234 students were quantified using SOFIT. Students engaged in more moderate-to-vigorous physical activity during swimming classes (52% plus or minus 9.9) than during nonswimming classes (40% plus or minus 17). As a consequence, we advocate the inclusion of swimming lessons in physical education. Because the average engagement in moderate-to-vigorous physical activity was lower than the recommended 50% in 41% of swimming classes and in 77% of the nonswimming classes, however, comprehensive efforts are needed to increase physical activity levels during both types of elementary physical education classes.