The principal, in programming a teacher, shall (1) keep the number of preparations to a minimum; (2) ability and qualifications being equal, follow the policy of rotation among qualified personnel in the matters of sessions, teaching, building assignments, special classes, honors and other modified classes and division rooms; (3) consider the teacher’s professional background and preparation; and (4) in elementary schools, ability and qualifications being equal, program teachers for the grade level at which they have the most experience, except that any teacher may request a change in grade level assignment.