I used something similar on the kids I coached in riding. We couldn't just send them home early.. parents PAY for those lessons and expect to get a full hour's worth of instruction. Considering that I got paid 12 bucks a kid and had 6 kids an hour, it's good money. The barn got 18 per kid per hour, by the way. At the barn, kids goofing off during lessons is not only disruptive, it's dangerous. If I have to threaten them with Santa not coming, so be it. All the parents were perfectly ok with it, one even told me that the little girl was getting a pony for Christmas, so I was to impress upon her the importance of behaving and paying attention.