On the undisputed facts of this record it is my opinion that plaintiff had failed to adduce sufficient evidence to justify relieving her of all burden of *691proof on the issue of negligence by application of the doctrine of res ipsa loquitur. Even that “simple, understandable rule of circumstantial evidence” (Ybarra v. Spangard (1944) 25 Cal.2d 486, 489 [1] [154 P.2d 687, 162 A.L.R 1258]) must be founded on proof rather than conjecture: as said in Nelson v. Douglas Pedlow, Inc. (1955) 130 Cal.App.2d 780, 784 [6] [279 P.2d 823], “The res ipsa loquitur doctrine is not intended to open the door for mere speculation as to the cause of an injury.” Here a necessary prerequisite for its application was a showing of facts sufficient to establish that the accident was more probably than not the result of defendant’s negligence, for “In the absence of such a probability there would be no basis for an inference of negligence which would serve to take the place of evidence of some specific negligent act or omission.” (Zentz v. Coca Cola Bottling Co. (1952) 39 Cal.2d 436, 443 [2] [247 P.2d 344].) As with all other elements of a plaintiff’s prima facie case, it is the plaintiff who has “the burden of establishing the elements which permit application of the res ipsa loquitur doctrine” (Danner v. Atkins (1956) 47 Cal.2d 327, 331 [3] [303 P.2d 724]). In my view, plaintiff in the case at bench has failed to sustain that burden; and by condoning such failure the majority opinion—when stripped of its tone of moral indignation—in effect holds defendant absolutely liable for this unexplained accident.
The governing law may be briefly stated. In order to show that the accident was more probably than not caused by defendant’s negligence, plaintiff must establish a probable violation of a duty of care owed to her by defendant. In the few reported cases involving a personal injury action against a private school by one of its pupils, the courts have implied that such duty of care may include (1) a duty to provide adequate supervision of the pupils’ activities (Martin v. Roman Catholic Archbishop (1958) 158 Cal.App.2d 64, 66[1a]-69[1b] [322 P.2d 31]), and (2) a duty—analogous to that of an occupier of land towards an invitee—to keep the school premises in a reasonably safe condition and state of repair (Perbost v. San Marino Hall-School (1948) 88 Cal. App.2d 796, 802 [9a]-804 [9b] [199 P.2d 701]); in each instance it was specifically observed that the school was not an insurer of the safety of its pupils, but could be held liable only for a violation of such duty. To this extent at least, the duties of care of a private school towards its pupils are similar to those of a public school. (See Pirkle v. Oakdale *692Union etc. School Dist. (1953) 40 Cal.2d 207, 210 [1] [253 P.2d 1] [adequacy of supervision]; Ziegler v. Santa Cruz City High School Dist. (1959) 168 Cal.App.2d 277, 280 [2]-283 [6] [335 P.2d 709], and cases there cited [dangerous or defective condition; see former Gov. Code, § 53051] ; see generally Notes, 86 A.L.R.2d 489; 160 A.L.R. 7; id. at p. 250.)
In the case at bench plaintiff fails to present sufficient facts from which it can be concluded that defendant more probably than not violated one or the other of the above mentioned duties of care. As to the condition of the premises, plaintiff offers only the statement that defendant’s school “consisted of a house and a little children’s playground with such play things as a swing and slide and similar paraphernalia.” There is no showing whatever that any of such paraphernalia was dangerous or defective for use as nursery school equipment; or that if it was, defendant had notice of such condition yet knowingly allowed it to continue “for such a period of time as would enable a reasonably prudent person to discover and remove it” (Perbost v. San Marino Hall-School (1948) supra, 88 Cal.App.2d 796, 803 [14]). Even in a case where the instrumentality that injured the plaintiff schoolchild was identifiable (Novack v. Los Angeles School Dist. (1949) 92 Cal.App.2d 169,172 [1] [206 P.2d 403] [plaintiff found lying in school playground pinned beneath an overturned wooden box ordinarily used to store athletic equipment] ), the court affirmed a judgment of nonsuit on this ground. Pointing out that “There was no evidence that the box was unstable or wobbly in its upright position on the playground at the place where the accident occurred or at any place thereon, or that it had ever fallen except when it was pushed over” and that “There was no evidence from which it could be inferred that the box fell by reason of weather conditions, or that it toppled over by reason of any instability of, or structural defect in, the box itself,” the court concluded that “The doctrine of res ipsa loquitur is not applicable here.” Likewise, where as in the present case plaintiff offers no evidence concerning the probabilities of the accident’s being caused by a dangerous or defective condition of defendant’s school equipment or premises, an insufficient showing has been made to justify invoking res ipsa loquitur on that ground.
The majority are silent on the matter of the condition of the premises, and hold only that defendant violated her “duty to exercise care in the supervision of the infants in her school, *693and to keep them under supervision at all times that they were at the nursery.” (Ante, p. 688.) On this point the majority disparage the relevance of decisions of our courts discussing the duty of supervision owed to grammar and high school pupils; but as the majority also acknowledge, the difference is “in degree” rather than in legal character. The majority’s statement (ante, p. 688) that “The supervision required must be commensurate with the age of the children and with their activities” touches on the true issue in this case. When is the supervision thus “commensurate?” Or, conversely stated, when is it not commensurate ?
The reported decisions answer this question by reference to established principles of the law of negligence, and hold that in any particular instance the standard of supervision required is that which an ordinarily prudent person would provide in the same circumstances. “The standard of care required of an officer or employee of a public school is that which a person of ordinary prudence charged with his duties, would exercise under the same circumstances.” (Pirkle v. Oakdale Union etc. School Dist. (1953) supra, 40 Cal.2d 207, 210 [1], and cases there cited; accord, Lehmuth v. Long Beach Unified School Dist. (1960) 53 Cal.2d 544, 552 [3] [2 Cal.Rptr. 279, 348 P.2d 887].) This principle serves also to delineate the scope of the school’s duty to supervise: as said in Woodsmall v. Mt. Diablo etc. School Dist. (1961) 188 Cal.App.2d 262, 267 [3] [10 Cal.Rptr. 447], to “require the constant supervision of all movements of pupils at all times ” is “ clearly not the law. A school district is required to exercise reasonable supervision over its students while the school is in session, but, even under such circumstances ‘the law does not make school districts insurers of the safety of the pupils at play or elsewhere.’ ” •(Italics added.) (Accord, Taylor v. Oakland Scavenger Co. (1938) 12 Cal.2d 310, 317 [7] [83 P.2d 948]; Rodrigues v. San Jose Unified School Dist. (1958) 157 Cal.App.2d 842, 845 [1] [322 P.2d 70]; Ford v. Riverside City School Dist. (1953) 121 Cal.App.2d 554, 562-563 [5] [263 P.2d 626], and cases there cited.)
The determination of what is “reasonable” supervision, of course, is essentially a factual issue: “There is no absolute rule as to the number of pupils one supervisor may adequately oversee, nor is there any fixed standard of supervision; the question as to compliance with the law is one for the determination of a jury under the facts of the particular case.” (Rodrigues v. San Jose Unified School Dist. (1958) supra, *694157 Cal.App.2d 842, 848 [6]; accord, Woodsmall v. Mt. Diablo etc. School Dist. (1961) supra, 188 Cal.App.2d 262, 266 [3]; Wright v. City of San Bernardino High School Dist. (1953) 121 Cal.App.2d 342, 345 [263 P.2d 25].) The foregoing rules govern equally a private school’s duty to supervise its pupils, for the law is no stricter in such case; indeed, the express declaration of Education Code section 13557 that “Every teacher in the public schools shall hold pupils to a strict account for their conduct on the way to and from school, on the playgrounds, or during recess” has been held inapplicable to a private school (Martin v. Roman Catholic Archbishop (1958) supra, 158 Cal.App.2d 64, 66-67 [2]).
The issue being therefore one of fact, the burden was on plaintiff—if she intended to invoke res ipsa loquitur—to present such facts as were available to show that the accident was more probably than not the result of the alleged inadequate supervision by defendant. But no such facts are presented ; instead, plaintiff offers only the conclusional statement that she was left “in [the] charge of and custody of the defendant. ’ ’ Plaintiff fails to present even the most elementary evidence—undoubtedly obtainable by discovery—to show what the circumstances of supervision were at defendant’s school: we are not told, for example, what supervisory facilities defendant held herself out as providing • how many other pupils attended the school; what was the teacher-pupil ratio ; whether the number of teachers (if there was more than one) remained constant throughout the day, or whether some worked on a part-time basis; what types of conduct and activities of the children were permitted; and whether the degree of supervision varied according to the particular activity being supervised. Even if plaintiff could not determine the precise cause of the accident, no reason appears why the foregoing facts, among others—if they had been favorable to plaintiff—could not have been discovered and presented to the court. In their absence there is no factual basis on which it can be determined that the accident was more probably than not caused by a failure of defendant to provide that degree of supervision which an ordinarily prudent person would provide “in the same circumstances,” for the simple reason that plaintiff has not informed the court what those circumstances were.
On this issue of duty to supervise the majority add nothing to plaintiff’s insufficient factual showing, beyond reiterating several times that plaintiff was healthy when delivered to the *695nursery school and injured when returned to her parents. It is settled, however, that the mere fact that an accident happened and an injury resulted does not, without more, warrant application of the doctrine of res ipsa loquitur. (See, e.g., Depons v. Ariss (1920) 182 Cal. 485, 488 [2] [188 P. 797]; Napolin v. Hotel Rose (1955) 137 Cal.App.2d 701, 708 [5] [290 P.2d 925]; Briscoe v. Pacific Elec. Ry. Co. (1948) 89 Cal.App.2d 439, 442-443 [3] [200 P.2d 875]; Hubbert v. Aztec Brewing Co. (1938) 26 Cal.App.2d 664, 668 [5] [80 P.2d 185, 1016].)
The majority also emphasize that the injury was “unusually” serious, and that “it certainly is not a matter of common knowledge that children normally come home from a nursery school with concussion of the brain and crossed eyes. ’ ’ (Ante, p. 690.) But the fact that a particular injury is rare and does not “normally” occur is not in itself proof that it was probably caused by the negligence of those in charge (see Siverson v. Weber (1962) 57 Cal.2d 834, 839 [6] [22 Cal.Rptr. 337, 372 P.2d 97], and cases there cited). Here it is undisputed that plaintiff was a healthy active child almost 4 years old—i.e., of an age and competency amply sufficient to enable her to walk, run, collide with other children or solid objects, climb, fall down, swing, jump, and generally conduct herself independently of the assistance and support of others, spending an entire nine-hour day at nursery school. All parents who raise normal children must know that in the ordinary course of indoor or outdoor play— especially in conjunction with a group of other children— a child such as plaintiff will often receive bumps, bruises, and scrapes or scratches on various parts of her body. Admittedly the blow here sustained by plaintiff had serious consequences; but this type of physical contact—-i.e., a bump on the forehead—-is among those commonly suffered by children of plaintiff’s age in many forms of active play, regardless of the supervision provided by parent or teacher. Indeed, in a case where the plaintiff schoolchild was able to specify in his complaint that his injuries were caused by the swinging of a bat by one of his fellow pupils while participating in a baseball game in the schoolyard (Underhill v. Alameda Elementary School Dist. (1933) 133 Cal.App. 733 [24 P.2d 849]), the court affirmed a judgment for the defendant school district after order sustaining a demurrer on the ground that no negligence was alleged, reasoning in part as follows (id. at p. 735 [1]) : “it is . . . a matter of common knowledge *696that children participating in such games and in fact in any form of play may injure themselves and each other and that no amount of precaution or supervision on the part of parents or others will avoid such injuries. The injuries which may result from the playing of said games are ordinarily of an inconsequential nature and are incurred without fault on the part of anyone. In such eases there is no liability and, of course, the fundamental rules governing liability remain the same even though the particular injury may prove to be of a more serious nature.” (Italics added.) Where, as here, the injury suffered by plaintiff may well have resulted from any one of a number of causes as diverse and unpredictable as the imagination or whim of plaintiff and her playmates, plaintiff has shown no factual basis from which it can be concluded that the accident was more probably than not the result of defendant’s negligence.
The insufficiency of plaintiff’s factual showing is underscored by the majority’s repeated reliance on assertedly “inferably false explanations” offered by defendant as to the cause of the injury. Just what are those “false explanations”? First, the majority make much of the meager fact that defendant informed plaintiff’s mother that plaintiff had wet her pants on the day in question; the majority declare that “This explanation is inferably false because counsel offered to prove that the child had stopped wetting her pants a year previously.” (Ante, p. 688.) Even though we are reviewing a judgment of nonsuit must we accept at 100 per cent face value counsel’s assertion that plaintiff had achieved unfailing bladder control at less than 3 years of age ? Is it not, rather, the common experience of parents that moments of fear, glee, excitement, or otherwise undampened enthusiasm may be marred by enuresis even in children who have long since “stopped” wetting their pants on a regular basis? Obviously the shock and fear occasioned by a blow such as plaintiff apparently received could well have resulted in the typically childish “accident” reported by defendant. And reference to it as an “accident” normally indicates a kind and understanding parent or caretaker. In any event, to characterize this report as an offered false “explanation” of plaintiff’s injury, as do the majority, is to presume further that a woman in charge of a nursery school could be so naive as to believe—or to expect that a child’s mother would believe—that wet pants cause concussion of the brain. Even the parents of plaintiff did not discover that the latter had *697any visible mark of injury until “At the dinner table at approximately 7:00 p.m. [plaintiff’s] father noticed that the child’s eyes were crossed. . . . The mother pushed the child’s hair away from the forehead, for the first time noticed a sizable round protruding bump on the child’s forehead.”
The majority brand as “another story, also inferably false” defendant’s sworn statement deposing that a fellow pupil struck plaintiff without warning as they were sitting in a group on the floor. The sole testimony offered to “disprove” that statement was to be that of a doctor—presumably in response to a hypothetical question—opining that it “would have been impossible” for a 5-year-old boy seated on the floor to have delivered with his bare hands a blow of sufficient force to have caused the subject injury. But such testimony would not necessarily prove defendant’s statement false: it remains true that the event described by defendant could well have occurred, for the testimony of the doctor would only tend to show that it could not have alone caused the brain concussion. Of course, expert testimony that a particular event could not have caused the injury does not resolve the question of determining the balance of probabilities as to what did cause the injury, or that any act or omission of defendant caused it.
It follows that defendant’s statements are not necessarily such barefaced lies as the majority imply; it is equally possible that defendant may not in fact have known the cause of the injury. At most, the statements are unsatisfactory explanations of how this accident happened; but it is not and should not be the law that the defendant is bound at his peril to produce a satisfactory explanation of the cause of the plaintiff’s injury, unless (which is not the ease here) the plaintiff has first sustained Ms burden of introducing facts sufficient to support an inference that the injury was more probably than not the result of negligence by the defendant. As Dean Prosser acutely observes, “if the facts give rise to no such inference, a plaintiff who has the burden of proof in the first instance could scarcely make out a case merely by proving that he knew less about the matter than his adversary.” (Prosser, Torts (2d ed. 1955) p. 209.)
In conclusion, under the threat of allowing any personal injury action brought against a nursery school to go to the jury on a mere showing (1) that an accident happened and a child was hurt and (2) that the school is unable to produce a satisfactory explanation of the event, the majority here place on such schools the burden of constant, unrelenting *698surveillance of every movement of every child during every moment the_child is in the schools’ custody, regardless of the type of activity in progress. This is a greater burden of supervision than even a parent ordinarily assumes; and it may be doubted that such a pervadingly adult-dominated atmosphere will be conducive to the development of a capacity for self-care, or of a sense of independence and emotional maturity, in the children involved.
I would affirm the judgment of nonsuit.
Traynor, J., concurred.