I am on the alli plan.  My physical activity is limited because I have a torn tendon.  I'm also a first grade teacher.  By the end of the day, It's too painful to do any physical activity, even standing.  What other physical activity could I do?

If the torn tendon is in your leg, what about doing things that work your upper body? Bicept curls, shoulder press, lateral raises all can be done while seated. Lean forward and do a reverse fly. If you have resistance bands they can be attached to a door knob and you can do a seated row.

Are you able to swim? If so, swimming would give you a great cardio workout.

Before you do anything, though, check with your doctor. They can be a great resource and explain what limitations you should have.