(a) Except as provided by Subsection (c), each classroom teacher or full-time librarian is entitled to at least a 30-minute lunch period free from all duties and responsibilities connected with the instruction and supervision of students. Each school district may set flexible or rotating schedules for each classroom teacher or full-time librarian in the district for the implementation of the duty-free lunch period.
(b) The implementation of this section may not result in a lengthened school day.
(c) If necessary because of a personnel shortage, extreme economic conditions, or an unavoidable or unforeseen circumstance, a school district may require a classroom teacher or librarian entitled to a duty-free lunch to supervise students during lunch. A classroom teacher or librarian may not be required to supervise students under this subsection more than one day in any school week. The commissioner by rule shall prescribe guidelines for determining what constitutes a personnel shortage, extreme economic conditions, or an unavoidable or unforeseen circumstance for purposes of this subsection.