Actually, I'm fairly certain that if the coach is receiving a paycheck from the district he's not allowed to charge to work with the kids that he's already being paid to work with.
Really, you think that it is ok for a coach at a public HS to get paid directly by parents? Depending on how you want to look at it, it is either bribery or extortion.
If you do not see a problem with HS coaches from public schools operating for profit programs where they strongly encourage/coerce kids/parents to pay them to play for them you are not being honest.