I wouldnt advocate "turning em loose" until they reach a certain point of maturity. That point differs from child to child and must be a decision of the teacher/parent.
BUT, a good quality .22 bolt action, like a crickett, adds a bit of "maturity" that helps to instill a special bit of confidence in the child. ALL kids yearn to be a "grown up" and do things like "dad/mom". A .22 goes "BANG" like Dads/moms gun and makes the child feel "special" and "all grown up". What this does is adds a bit of "fun" into the equation and helps to make the child yearn to get back to the range with the adult again.
air guns, altho a great starting point and very accurate, get old and seem "weak" after a time, especailly after being introduced to real "boom" sticks and the child wants to have a "real" gun to shoot.
"Those that would trade essential liberty for temporary security deserve neither liberty nor security." - Benjammin Franklin
The 1911: Turning useless trash into good fertilizer for over 100 years!!