We put a lot of restrictions on minors and what they can do or be done to. On top of that, some things which would be ok in a different setting would be inapropriate and disruptive in a classroom environment.

Also, with regards to the motivational aspect, I would not expect a toddler to be able to make the appropriate choice between a healty meal and candy. I do not expect a teen to be able to restrain themselves from the pubescent games of social media prancing and paying attention to the class teaching.