The newspaper's unidentified source said Monday a surveillance camera tape shows Manchester High student Malvrick Donkor, 14, who died last Wednesday, climbing down a ladder into the pool's deep end.
"There's no splashing, no flailing like you would typically think of," said the source, who watched the videotape. "He just slipped under water. Other kids were swimming over the top of him, not knowing he was down below."
It wasn't until the class ended that a student spotted Malvrick and told the teacher, who dove in and pulled the boy out, the source said.
Interim School Superintendent Richard Kisiel said he could not comment while the death is investigated.
Kisiel said the swim class teacher, Thayer Redman, is on paid administrative leave.
The school has closed the pool and halted swim classes, the newspaper said.
A vigil for Malvrick outside the school Monday night attracted several hundred people.