How have the courts interpreted expert testimony in the context of supervision of playgrounds?

From the record it appears that both experts were qualified by years of experience and study to testify generally as to supervision of playgrounds. Neither witness stated dogmatically the number of pupils one person could properly supervise and neither testified in such manner as to eliminate from consideration special problems which might be involved in any particular instance. Their testimony was general in nature and restricted in great part to usual school conditions. The case of Charonnat v. San Francisco Unified School Dist., 56 Cal.App.2d 840, 133 P.2d 643, is relied upon by appellants to show that one witness' testimony was in error. That case reveals unusual facts and differs completely from the one here considered. Appellants' arguments as to the expert testimony are directed against its weight and credibility. These were matters for the jury to consider. Appellants at the time of trial cross-examined these witnesses, and appellants' present [157 Cal.App.2d 848] contention that the customs testified to by the experts were below the standard required by law and hence inadmissible arise from the same view of the evidence as that presented in their first argument. Granting that if evidence of custom does not measure up to the standard required by law it is inadmissible, nevertheless, there is nothing in the expert testimony here which shows a custom that was of a lower standard than that required by law. 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.