(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.