The gruesome accident followed the warnings of a security guard on the bus who said he told the teens repeatedly not to open the hatch.
Daniel Fernandez, 16, was among 65 teens aboard the bus Friday night from New York City on its way to the party in Garfield, N.J., said Steve Coleman, spokesman for the Port Authority of New York and New Jersey.
The teens were dancing and the bus had gotten hot, the security guard, Alex Franco, told the Daily News. Still, he said, he had asked the teens to leave the emergency hatch alone. "I told them not to open the hatch, like three or four times, but kids, they don't understand," he said.
Fernandez's English teacher at St. Francis Preparatory School in Queens echoed that sentiment.
"Sometimes kids don't recognize their own mortality," said Jane Lynch, her voice trembling.
Franco said he had gone downstairs to tell the driver that it was getting too hot.
"Two, five minutes I was downstairs," he said.
But then he heard teenagers screaming, and he saw Fernandez on the floor of the bus. "There was so much blood everywhere," he told The New York Post.
Fernandez, who lived in Queens' Woodside neighborhood, was pronounced dead at a hospital.
He was a beloved student, said Lynch, who taught him last school year.
"He was an adorable, low-key kid, with a sweet smile," she said. "Kids loved him; he had lots of friends and was popular with the girls."
She said a group of students had a special last project, producing and appearing in a takeoff on the novel "Lord of the Flies," about a group of boys on a desert island who try to govern themselves, with disastrous results.
"He was very hands-on, he took the leadership role," said Elizabeth Gonzalez, a student teacher at St. Francis last year.
Fernandez played the villain in the video students posted on YouTube, she said.
In class, "he was very lively, and high-spirited," she said. "And he had so much potential in his writing."
The school said on its website that it shared in grief and shock over his death. A wake was set for Monday, the site said.
Designer Limousines, which operates the bus, expressed its "deepest heartfelt sympathy" to the teen's family. The company said it would conduct an internal investigation.
Calls to the Fernandez family home in Queens rang unanswered.