So the HR manager of the Board calls you and says that the Board has decided that you can no longer be in the school. Well that would take some formal action by the Board to implement. That means that at one of their meetings they would have had to discuss the issue (perhaps as a matter in closed session) then come out of closed session and placed their decision on the record and why they made that decision.
Obviously, they did not hear from you in their deliberations and you have no idea what this teacher told the Board.
So, I'm not going to preempt the attorney you will be seeing but I would be writing a letter to the BOE asking for the records of discussion and the action they took for starters. The BOE is subject to your state's sunshine law (open public meeting law) and they have to conduct their business in accordance of it.
A call from the HR manager has absolutely no authority here.

