Appointment-Salaries-Payment-School month-School term.) School boards shall appoint all teachers, determine qualifications of employment and fix the amount of their salaries subject to limitation set forth in this Act. They shall pay the wages of teachers monthly, subject, however, to the provisions of Section 24-21. The school month shall be the same as the calendar month but by resolution the school board may adopt for its use a month of 20 days, including holidays. The school term shall consist of at least the minimum number of pupil attendance days required by Section 10-19, any additional legal school holidays, days of teachers’ institutes, or equivalent professional educational experiences, and one or two days at the beginning of the school term when used as a teachers’ workshop.