The accounting system used to record the financial affairs of any school district shall be designed to provide separate recording and clear distinction between expenditures for salaries of classroom teachers employed by the district and expenditures for other purposes of the district. As used in this

section “salaries of classroom teachers” means: (

a) The salary paid to each teacher employed by the district whose duties require that the full time for which the teacher is employed be devoted to the teaching of pupils of the district. (

b) The portion of the salary of each teacher whose duties require that a part, but not all, of the full time for which the teacher is employed be devoted to the teaching of pupils of the district, which is equal to the portion of such full time actually devoted by the teacher to teaching pupils of the district. (

c) The salary paid to each instructional aide employed by the district, any portion of whose duties are required to be performed under the supervision of a classroom teacher. As used in this

section a “teacher” means an employee of the district employed in a position requiring certification qualifications and whose duties require him to teach pupils of the district for at least one full instructional period each schoolday for which the employee is employed. In the case of a teacher employed to teach in an elementary school, an instructional period is a period of not less than minutes. In the case of a teacher employed to teach in a secondary school, an instructional period is the number of minutes equal to the number of minutes of the regular academic period in the junior high school, or high school, in which the teacher is employed to teach.