In the event a teacher, not already employed in a school, is assigned to such school, the county superintendent of education shall give to the trustees of said school notice in writing of such assignment, and the trustees of said school, within 10 days from the date of the receipt of the superintendent’s notice of assignment, may by unanimous consent refuse to accept the assignment of such teacher to their school upon written notification to the county superintendent of education setting out the reason for such refusal; and it is hereby made the duty of the county superintendent of education to assign another teacher to such school.