Measurement of children’s physical activity in the past decade has moved out of the laboratory and into the field. One of the most common field measures used by teachers and researchers is the heart rate monitor. These devices allow students to receive feedback and monitor their levels of physical activity in the form of heart rate measures. While it is common for teachers to use heart rate monitors during fitness units, it is less common to see them used during sports activities. We examined the question “Do heart rate monitors influence student activity levels when the focus of lesson objectives includes skill and tactical skill development in addition to maintaining moderate to vigorous physical activity for 50% of the lesson?” Data were collected using Computer Science Application (CSA) uniaxial accelerometers worn on the hip. Students in two elementary school classes, a composite 3rd-4th grade (Girls N=3, Boys N=2) and 5th grade (Girls N=3, Boys N=3) participated in the study. Each class was located in a different school. Lessons were taught by two board-certified, experienced, master physical education teachers. During an eight -day team handball sport education unit, students wore heart rate monitors for four of the days. The days when students wore the heart rate monitors were randomly selected for each school. Heart rate monitors were set to product an audio prompt if students moved out of their target heart rate zone. Comparisons using mean CSA counts per minute collected from the accelerometers were assessed using a single subject alternating treatment experimental design (Cooper, Heron & Heward, 1987). Results show that (a) neither condition (i.e., wearing or not wearing a heart rate monitor) was more effective than the other in increasing student activity levels, (b) there were substantial differences between males and females activity levels (differences between 1000-2000 CSA counts per minute), (c) there were minimal differences in terms of the ability of the students and their level of physical activity. The results suggest that the effectiveness of the teacher rather than the heart rate monitor was responsible for student activity levels. Data also demonstrate that despite small-sided games, mixed-ability teams, mixed-gender teams, and developmentally appropriate instruction, girls who participated in the study had lower levels of physical activity than boys.