(1)    In this section “teacher” means any person who holds a teacher’s certificate or license and whose legal employment requires such certificate or license, who is employed full time and meets the minimum requirements prescribed by the governing body employing such person and who is employed by a school board, board of trustees or governing body of any school operating under chs. 115 to 121 and lying entirely and exclusively in a county having a population of 750,000 or more. “Teacher” does not include any superintendent or assistant superintendent; any teacher having civil service status under ss. 63.01 to 63.17; any teacher in a public school in a 1st class city; or any person who is employed by a school board during time of war as a substitute for a teacher on leave while on full-time duty in the U.S. armed forces or any reserve or auxiliary thereof and who is notified in writing at the time of employment that the position is of a temporary nature.

   (2)   All teachers shall be employed on probation, but after continuous and successful probation for 3 years and the gaining of the 4th contract in the same school system or school, their employment shall be permanent except as provided in sub. (3). All principals shall be employed on probation, but after continuous and successful probation for 3 years and the gaining of a 4th contract in the same school system or school, their employment shall be permanent except as provided in sub. (3). Upon accepting employment in another school system or school to which this section applies, a teacher who has acquired permanent employment under this section shall be on probation therein for 2 years. After continuous and successful probation for 2 years and gaining the 3rd contract in such school system or school, employment therein shall be permanent except as provided in sub. (3). A person who acquired tenure as a teacher under this section shall not be deprived of tenure as a teacher by reason of the person’s employment as a principal.

   (3)   No teacher who has become permanently employed under this section may be refused employment, dismissed, removed or discharged, except for inefficiency or immorality, for willful and persistent violation of reasonable regulations of the governing body of the school system or school or for other good cause, upon written charges based on fact preferred by the governing body or other proper officer of the school system or school in which the teacher is employed. Upon the teacher’s written request and no less than 10 nor more than 30 days after receipt of notice by the teacher, the charges shall be heard and determined by the governing body of the school system or school by which the teacher is employed. Hearings shall be public when requested by the teacher and all proceedings thereat shall be taken by a court reporter. All parties shall be entitled to be represented by counsel at the hearing. The action of the governing body is final.

   (4)   If necessary to decrease the number of permanently employed teachers by reason of a substantial decrease of pupil population within the school district, the governing body of the school system or school may lay off the necessary number of teachers, but only in the inverse order of the appointment of such teachers. No permanently employed teacher may be prevented from securing other employment during the period that the teacher is laid off under this subsection. Such teachers shall be reinstated in inverse order of their being laid off, if qualified to fill the vacancies. Such reinstatement shall not result in a loss of credit for previous years of service. No new permanent or substitute appointments may be made while there are laid off permanent teachers available who are qualified to fill the vacancies.

   (6)   This section does not apply after December 21, 1995. Any person whose employment is permanent under sub. (3) on December 21, 1995, shall retain all of the rights and privileges of such permanent employment after that date.