But what the school allegedly did after is shocking.
Teenager Larryn Watkins spent almost a minute lying face down in the water before anyone, including the supervising parents, noticed there was something wrong.
The incident took place in Buffalo, New Jersey, on Tuesday.
The 13-year-old is now in an induced coma in a local hospital.
According to 7 Eyewitness News, the teenager was quickly pulled from the water by a lifeguard while others performed CPR.
One witness, Julienne Kuty, who filmed the incident, told the station that she heard a woman yell, “Is he OK? Is he OK?.
“Then she walked away,” she said. “Then I saw a lifeguard jump in and pull the boy out of the pool.”
Ms Kuty said her daughter-in-law, a nurse, helped to resuscitate the boy when he regained consciousness.
“My son came up with 57 seconds that he was actually under the water,” she added.