All instructors, excluding vocational staff cooperating with the State Department of Career and Technology Education, shall be provided planning time each week as required by the State Accreditation Standards within the student school day for preparation. Elementary and middle school teachers with 200 minutes will be provided 200 minutes for planning each week. Secondary teachers are to be provided 225 minutes for planning each week. The preparation period may be used for the following duties: personal instructional preparation; planning, selecting, and preparing materials for instruction; conferring with parents, staff, and administrators; keeping school records; supervising aides (if assigned); grading student papers and recording student grades; and study of current literature to keep abreast of developments within the subject matter taught by the teacher. The preparation period shall be utilized within the building of major assignment and for the purposes indicated. Teachers shall leave the school premises only to carry out functions relating to the above duties when written permission to do so has been obtained from the building principal.