Any district school board may enter into contracts of insurance for liability or operate a self-insurance program for liability covering all activities engaged in by the district for medical and hospital benefits for students engaging in athletic contests and in traffic patrols and may pay the necessary premiums thereon. Failure to procure such insurance or operate such a program shall in no case be construed as negligence or lack of diligence on the part of the district school board or the members thereof. [Formerly 332.235; 1967 c.627 § 13; 1997 c.795 § 2]