Where do you think the $20 million will come from? It comes from the TAXPAYERS, not the school district or any of its employees. Thus, the school district and union will have no motivation to change because none of its employees are held PERSONALLY accountable.
You want to make things change? Criminally charge and prosecute school district and union staff, and management as accessories to assault and the other criminal acts being perpetrated. Once school district and union staff and management understand there are PERSONAL consequences to them for their behavior, things will change - not before.
Then let the taxpayers deal with the school district and the union. It may take some time, but it will eventually get done.
Look at the case of that woman in New York who died of a heart attack when the cops raided the wrong apartment in a drug raid. The cops themselves are probably not going to be held personally liable in this case, but the City of New York immediately changed the procedure for drug raids of this sort.