How long should a child wait to go back to school after getting his appendix taken out?

Depends. Removal of the appendix is only part of the story. Ruptured at removal or not? Removed by open excision, or thru an endoscope? Delay until normal feeding & stooling?These factors influence a expected return to regular activities. Your surgeon should describe the milestones the kid should meet before returning to school.
1-2 weeks. Recovery from appendectomy is dependent on the extent of disease, nature of the surgery, and health of the patient. Uncomplicated appendicitis rx'd by laparoscopic surgery...1week max; add a few days if the traditional operation. If the appendix was ruptured, your child might not have their energy back to normal for 2 weeks. A good gauge is when they don't need a mid-day nap.