There are plenty of ways to get some extra fitness at school, especially if you never have time after school. 

• Take the long way to get to class
• Use the stairs instead of the elevator
• Use your books or backpack as weights
• Offer to walk a friend to their class before going to yours
• Suspend your feet just slightly above the floor when sitting for a few seconds at a time
• Do clenches with your thighs and abdomen

And of course only do these things if time permits and they don’t interfere with your studies. Otherwise, get creative and get “school” fit!