If any school building be abandoned for use for school purposes, the board may cancel or reduce all insurance carried by it on such abandoned school building and its contents, and the board shall not be required to renew existing insurance or write any insurance on any such building and its contents, the use of which for school purposes has been discontinued; provided, that at least ten days before the cancellation or reduction of any such insurance the board shall give notice to the proper authorities that such cancellation or reduction is to be made.