The law regarding the duty of supervision on school premises is very well established. "It is the duty of the school authorities to supervise at all times the conduct of the children on the school grounds and to enforce those rules and regulations necessary to their protection. The school district is liable for injuries which result from a failure of its officers and employees to use ordinary care in this respect. " (Taylor v. Oakland Scavenger Co. (1941) 17 Cal.2d 594, 600 (Taylor).) "What is ordinary care depends upon the circumstances of each particular case and is to be determined as a fact with reference to the situation and knowledge of the parties." (Bellman v. San Francisco H. S. Dist. (1938) 11 Cal.2d 576, 582.) Regarding that requirement of ordinary care, the court stated: "Although a school district is not an insurer of its pupils' safety , our cases have long established that a school district bears a legal duty to exercise reasonable care in supervising students in its charge and may be held liable for injuries proximately caused by the failure to exercise such care. We recently reaffirmed this rule in Dailey v. Los Angeles Unified Sch. Dist. (1970) 2 Cal.3d 741, 747, declaring that 'California law has long imposed on school authorities a duty to "supervise at all times the conduct of the children on school grounds and to enforce those rules and regulations necessary to their protection." The standard of care imposed upon school personnel in carrying out this duty to supervise is identical to that required in the performance of their other duties. This uniform standard to which they are held is that degree of care "which a person of ordinary prudence, charged with [comparable] duties, would exercise under the same circumstances." ' In Dailey, two unsupervised high school students engaged in 'slap-boxing' in the school gym during lunch hour, and as a result, one of the students fell, struck his head, and died shortly thereafter. 'Slap-boxing' is a rough and forbidden game which, according to the testimony of other students, was never played when a teacher was nearby. In reversing a directed verdict in favor of defendant school district, this court held that the issues of whether or not the school acted negligently in failing to provide adequate supervision of the lunch hour recess and, if so, whether the student's injuries were proximately caused by such negligence, fell within the province of the jury." (Hoyem v. Manhattan Beach City School District (1978) 22 Cal. 3d 508, 513.) The duty of care imposed on a school district towards its pupils arises from their special relationship. Not all students attend education classes that are mandatory. The Hoyem court noted that parents place trust in schools to supervise their children and "[a] large number of working parents enroll their children in summer school because they cannot afford alternative adult supervision. Surely these parents may legitimately expect adequate supervision." (Hoyem, supra, 22 Cal.3d at p. 519.)