In our case, it was really obvious. Our DS6 came home from 1st grade on his first day of full-day school, threw down his backpack and said, "I'm *never* going back! If you make me go back to 1st grade, then I won't go to 2nd grade because it will be even LONGER and MORE BORING!!!"
He had been sunny and easygoing his whole life, but his personality changed drastically as soon as school started. He began to get in trouble in school, something that our highly rule-oriented son would never have done before; he'd have rather died than get in trouble in preschool or half-day K. His greatest source of pride in K was that his behavior traffic light never went to yellow, let alone red, for the entire year. Missing recess because of bad behavior? That was a serious cry for help! We pulled him out to home school, and his personality returned to pleasant almost immediately. It was like magic!
Basically, if the challenge increases and the behavior improves, you know that there's a direct correlation.
