Section 118.21 - Teacher contracts(1) The school board shall contract in writing with qualified teachers. The contract, with a copy of the teacher's authority to teach attached, shall be filed with the school district clerk. Such contract, in addition to fixing the teacher's wage, may provide for compensating the teacher for necessary travel expense. A teaching contract with any person not legally authorized to teach the named subject or at the named school shall be void. All teaching contracts shall terminate if, and when, the authority to teach terminates.(2) Any person who contracts to teach in any public school shall file in the office of the school district administrator, within 10 days after entering into such contract, a statement showing the date of expiration, if any, and the grade and character of certificate or license held. In any school district not having a school district administrator, the statement shall be filed with the school district clerk. Teachers employed by a cooperative educational service agency shall file the statement in the office of the agency coordinator. No order or warrant may be issued by the school district clerk in payment of the salary of any teacher, unless the teacher has complied with this subsection.(3) School boards may provide in the contracts of teachers of agricultural and homemaking courses for payment out of school district funds for services performed outside the school district and connected with the performance of their regular teaching duties, and for travel expenses connected with such services.(4) School boards may give to any teacher, without deduction from the teacher's wages, the whole or part of any time spent by the teacher in attending a teachers' educational convention, upon the teacher's filing with the school district clerk a certificate of attendance at the convention, signed by the person or secretary of the association conducting the convention.Amended by Acts 2017 ch, 59,s 1525, eff. 9/23/2017.1979 c. 301; 1993 a. 492. A collective bargaining provision that releases only teacher members of a majority union from in-service days to attend, with pay, a state convention of the union is discriminatory, but the school board can deny compensation to minority union members who attend a regional convention of their union if they do so in good faith. Board of Education v. WERC, 52 Wis. 2d 625, 191 N.W.2d 242 (1971). A teacher's lack of legal authority to teach assigned courses, although known to the school board at time of hiring and subsequent assignments, was sufficient ground for dismissal despite the fact that school superintendent repeatedly assured the teacher that the certification problem was an administrative omission that would be cured by the board. Grams v. Melrose-Mindoro Jt. School Dist. No. 1, 78 Wis. 2d 569, 254 N.W.2d 730 (1977). An individual teacher's contract under this section and s. 118.22 is subservient to a collective bargaining contract under s. 111.70. 60 Atty. Gen. 342. School boards have authority to contract with teachers to provide for an increment or sum in addition to their regular salary in return for the teacher choosing an early retirement option. 63 Atty. Gen. 16. Even though a teacher was properly dismissed for an admitted violation of school rules, she was entitled to a due process hearing on other charges affecting her reputation as a teacher. Carpenter v. Greenfield School Dist. No. 6, 358 F Supp. 220 (1973).