A contract between a board of school directors and a teacher shall not be valid unless the same is in writing, or partly written and partly printed, in triplicate, and signed by the teacher and by a majority of the board or by a member of the board or other person who has been duly authorized by a majority vote of the board at a regular meeting to sign the contract in question on behalf of the board. One copy thereof shall be filed with the board, one copy delivered to the teacher, and one copy delivered to the superintendent. Such contract shall specify the date when the teacher shall begin service, the time, grade, and date of expiration of the license held by the teacher, the salary of the teacher and such other matters as may be necessary for a complete understanding between the parties. (Amended 1989, No. 118, § 3.)