(a) Except as hereinafter otherwise provided, all school districts and career and technical school districts shall pay all regular and temporary teachers, supervisors, directors and coordinators of career and technical education, psychologists, teachers of classes for exceptional children, supervising principals, career and technical teachers, and principals in the public schools of the district the minimum salaries and increments for the school year 1968-1969 and each school year thereafter, as provided in the following tabulation in accordance with the column in which the professional employe is grouped and the step which the professional employe has attained by years of experience within the school district each step after step 1 constituting one year of service. When a school district, by agreement, places a professional employe on a step in the salary scale, each step thereafter shall constitute one year of service. When a district adopts a salary scale in excess of the mandated scale, it shall not be deemed to have altered or increased the step which the employe has gained through years of service.

(b) Professional employes shall be grouped in the following columns:

Class A. Teachers holding a standard certificate valid for the subject or grades in which the teacher is giving instruction.

Class B. Teachers holding a college certificate valid for the subjects or grades in which the teacher is giving instruction.

Class C. Teachers of classes approved by the Department of Education for exceptional children holding a standard certificate valid for the subjects or grades in which the teacher is giving instruction.

Class D. Teachers of classes approved by the Department of Education for exceptional children holding a college certificate valid for the subjects or grades in which the teacher is giving instruction.

Class E. Supervisors, directors and coordinators of career and technical education, who devote one-half or more of their time to supervision of instruction, and psychologists, holding a standard or college certificate.

Class F. Principals, who devote one-half or more of their time to supervision and administration and having less than twenty (20) teachers under their supervision, who hold a standard certificate, or college certificate.

Class G. Such principals, having twenty (20) or more teachers under their supervision, but less than forty (40), and who hold a standard certificate, or college certificate.

Class H. Such principals, having forty (40) or more teachers under there¹ supervision, but less than sixty (60), and who hold a standard certificate, or college certificate.

Class I. Such principals, having sixty (60) or more but less than eighty (80) teachers under their supervision, and who hold a standard certificate, or college certificate.

Class J. Such principals, having eighty (80) or more teachers under their supervision, and who hold a standard certificate, or college certificate.

Class K. Supervising principals, having less than forty (40) teachers under their supervision, and who hold a standard certificate, or college certificate.

Class L. Supervising principals, having forty (40) or more teachers under their supervision, but less than sixty (60), who hold a standard certificate, or college certificate.

Class M. Supervising principals, having sixty (60) or more but less than eighty (80) teachers under their supervision, and who hold a standard certificate, or college certificate.

Class N. Supervising principals, having eighty (80) or more but less than one hundred (100) teachers under their supervision, and who hold a standard certificate, or college certificate.

Class O. Supervising principals, having one hundred (100) or more teachers under their supervision, and who hold a standard certificate or college certificate.

Class P. Career and technical teachers, holding a standard or college certificate valid for the subjects or grades in which the teacher is giving instruction, and who is employed for the entire calendar year because of seasonal activities.

(e) In the case of any professional employe or temporary professional employe who holds a Master's Degree or its equivalent, two (2) additional steps of three hundred dollars ($300) each shall be added to his class.

(f) The mandated salaries provided in this section shall be applicable to all professional and temporary professional employes within their respective class. The annual salaries payable under this section for the school year 1968-1969 and each school year thereafter, shall include an annual service increment for service in the school district during the previous school year by advancing the salary of the professional or temporary professional employe at least one full step on the minimum salary schedule or to the step on which he is entitled to be placed by virtue of years of experience within the school district, whichever is higher.

(g) Any professional employe or temporary professional employe who holds a Master's Degree or its equivalent shall be placed on a step which shall be at least three hundred dollars ($300) in addition to the minimum salary of an employe who holds a college certificate and who does not hold a Master's Degree and who has the same number of years of service in the district.

(h) The salaries and increments provided by this section may be reduced by written agreement between the school district and the employe for the purpose of the school district purchasing a tax-sheltered annuity contract, a retirement income endowment policy, or other similar annuity contract. The reduction shall not exceed the premium for the annuity.