The foregoing schedules prescribe a minimum salary in each instance, and where an increment is prescribed, it is also a minimum. It is within the power of the boards of school directors to increase for any person or group of persons, included in any schedule, the initial salary or the amount of an increment or the number of increments.

Nothing contained in this act shall be construed to interfere with or discontinue any salary schedule rights, tenure rights, or other privileges or terms of employment now or heretofore in force in any school district, provided such shall meet the requirements of this act, nor to prevent the adoption of any salary schedule in conformity with the provisions of this act.

In addition to the salaries provided for by this act, the board of directors of each school district is hereby authorized to grant temporary or emergency increases in salaries to members of its teaching or supervisory staff for any period, and to discontinue such increases at the end of the period for which the same were granted, any law to the contrary notwithstanding. In order to pay the amount of salary hereby provided for, the board of school directors of any school district may revise its budget by increasing its appropriation or appropriations for salaries of members of the teaching and supervisory staffs of¹ the school district for any year. The funds therefor shall be provided from unexpended balances in existing appropriations, from unappropriated revenue, if any, or from temporary loans. Any temporary or emergency increases heretofore or hereafter granted by any school district, and the discontinuance thereof at the end of the period for which granted, and any contracts, rights, tenure rights, or other privileges or terms of employment heretofore in effect in any school district, provided the same shall meet the requirements of this act, are hereby ratified, confirmed and made valid, notwithstanding the terms or provisions of any other act or that the same may have been done without previous authority of law.

No school district shall be required to pay any increments provided for hereby to any teacher who is rated unsatisfactory for any part of the probationary period of such teacher.