The board of education of a school district may modify an indefinite contract annually on or before the fifteenth day of May in the following particulars:

1. (1) Determination of the date of beginning and length of the next school year;
2. (2) Fixing the amount of annual compensation for the following school year as provided by the salary schedule adopted by the board of education applicable to all teachers. The modifications shall be effective at the beginning of the next school year. All teachers affected by the modification shall be furnished written copies of the modifications within thirty days after their adoption by the board of education.

(L. 1969 p. 275 § 168.105, A.L. 1990 S.B. 740)

(1993) The protection of the Teacher Tenure Act extends to only those provisions in teacher-school district contracts that cover teaching duties, being only those duties that require a teaching certificate. This act does not prevent a school board from unilaterally eliminating from a teacher's contract his extra and extended duties and the pay therefor. Sadler v. Board of Education of Cabool School District R-4, 851 S.W.2d 707 (Mo. App. S.D.).