1. An indefinite contract with a permanent teacher shall not be terminated by the board of education of a school district except for one or more of the following causes:
(1) Physical or mental condition unfitting him to instruct or associate with children;
(2) Immoral conduct;
(3) Incompetency, inefficiency or insubordination in line of duty;
(4) Willful or persistent violation of, or failure to obey, the school laws of the state or the published regulations of the board of education of the school district employing him;
(5) Excessive or unreasonable absence from performance of duties; or
(6) Conviction of a felony or a crime involving moral turpitude.
2. In determining the professional competency of or efficiency of * a permanent teacher, consideration should be given to regular and special evaluation reports prepared in accordance with the policy of the employing school district and to any written standards of performance which may have been adopted by the school board.