Rufus, although the Jim Evans Balk Video is directed toward Umpires. It is a great tool to use in understanding what a balk is or is not.
I would suggest getting a copy to help you coach, since we as umpires use this as a training tool in recognizing balks. It covers pirmarily OBR, however there are references to NFHS and NCAA that will help.
You can order a copy at
http://www.umpireacademy.com/store/p...products_id=30