230.31  Secretary and executive officer of the school board.--The superintendent shall be the secretary and executive officer of the school board; provided, that when the superintendent of any district is required to be absent on account of performing services in the volunteer forces of the United States or in the National Guard of the State or in the regular Army or Navy of the United States, when the said superintendent shall be called into active training or service of the United States under an Act of Congress or pursuant to a proclamation by the President of the United States, the superintendent shall then be entitled to a leave of absence for not to exceed the remaining portion of the term for which he or she was elected.