As noted in "How to Prove Your School Negligence Case Under New York Law," while children are in school and during school hours, the school stands in the role of the child's parent, and is charged with the responsibility (or, in legalese, the "duty") to "exercise such care of them as a parent of ordinary prudence would observe in comparable circumstances'" (Mirand v City of New York, 84 NY2d at 49, quoting Hoose v Drumm, 281 NY 54, 57-58; see Swan v Town of Brookhaven, 32 AD3d 1012, 1013; Doe v Orange-Ulster Bd. of Coop. Educ. Servs., 4 AD3d 387, 388).
As New York State's highest court observed in Mirand, "The duty owed derives from the simple fact that a school, in assuming physical custody and control over its students, effectively takes the place of parents and guardians" (Mirand v City of New York, 84 NY2d at 49).
But what happens once the "official" school day ends? Does the school's duty change?
The answer is that it depends on the nature of the after-school activity: if it is a student's "voluntary participation in an intramural or extracurricular school sport," then the school will only be duty-bound to act as a reasonably prudent person under similar circumstances; but if the activity on the other hand, the activity is an academic class for which the participants would receive a grade, then the school will still be held to the higher standard of a reasonably prudent parent.
Parenthetically, there are other circumstances under which a school can still be held liable for injuries to its students under New York law - even outside school. For additional information on that topic, please see "How New York Schools Can Be Held Liable in Negligence - Even For Accidents That Occur Off School Grounds."