Overall, I saw an increase in productivity in the work done after exercise. However, is the sacrifice to work out worth the reduced, but more focused, study that it offers? In order to experience this increased energy while studying, I had to sacrifice two hours when I could also be studying.
In conclusion, I would recommend light exercise before studying/class IF you have the time and there is not something urgent that needs to be done. In all, its a great tool if there is nothing else that you need to be doing.