East Hartford Fire Chief John Oates says the boy was found unresponsive in East Hartford High's pool on Wednesday afternoon.
School Superintendent Mark Zito says the drowning remains under investigation. He says grief counselors will be provided to students, faculty and staff, and he extended his sympathies to the student's family and friends.
The student's identity wasn't immediately disclosed.
Emergency crews received a report at around 12:30 p.m. of an unresponsive student in the pool. The superintendent says that a bystander was performing CPR when rescuers arrived and that the teen was taken to a hospital.
An autopsy was planned to determine if any medical factors were involved in the boy's death.