The law will not be specific to schools - it will be a question of whether ANYONE is allowed to make a tape recording of a conversation without both parties being aware of it. Teacher/parent, employer/employee, next-door neighbor/next-door neighbor, store manager/customer, you name it. Some states say it's all right as long as one party to the conversation is aware of the recording being made; others say both parties must be aware. I personally only know the law for my own state. But at IAAL says, since you failed to provide the state where you are, no one will be able to give you any additional information.