We got to skip out on "half-days" at school year round to help with cattle or crops.  Complete waste of distric money to send kids to school for only 4 hours and have an 8 minute class change every 52 minutes.  I wouldn't dream of letting a 12yr old alone in the combine while I drive off with the grain cart.  Hopefully you remind him several times never to get out of the machine with the header running.