We have purchased the Polar Cardio GX Heart Rate Monitor System. All students wear the heart rate monitors during class and their heart rate and the zone they are in is projected on the gym wall. This keeps them accountable for staying active. After class, the data is downloaded into the system and is saved for grading. We use this as their participation grade because the numbers don't lie. Also the results can be directly emailed to their parents, if they have a question about grades! I love that I am not questioned about students grades because they get what they work for!