Maren Sanchez was attacked in the hallway of Jonathan Law High School in Milford, about an hour's drive from New York City, around 7:15 a.m. Staff members and paramedics performed life-saving measures on the girl, but she was pronounced dead at a hospital, police said.
The 16-year-old boy was taken into custody. His name wasn't released because of juvenile offender laws, said Police Chief Keith Mello. Investigators were looking into reports that the girl had declined to be his date for the junior prom, which was scheduled for Friday night but was postponed because of the stabbing.
Sanchez, a junior, was in the National Honor Society and engaged in school activities, schools Superintendent Elizabeth Feser said. Students were released from school early, and officials were offering counseling services.
"We are obviously devastated by the loss of one of our students, Maren Sanchez," Feser said at a news conference. "She was a 16-year-old junior - vibrant, very, very involved in Jonathan Law High School, an incredible contributor, someone who was loved and respected."
Students described an emotional, somewhat chaotic scene as police and paramedics swarmed the school.
Sarah Golden, a 14-year-old freshman, said she was sitting in the main lobby with friends when she was startled by several security guards running down the hall. Then she heard a voice on a walkie-talkie say that someone had been strangled.
"I was trying not to freak out because it was really scary," Sarah said. "I just don't believe that something like that happened at my school. It's something that seems so unreal."
Golden's 17-year-old sister, Rebecca, a senior at the school, said she saw the victim lying on the floor surrounded by teachers, some of whom were crying. She said she didn't know what was going on at the time, and teachers directed her away from the victim.
Mello said Sanchez had a severe neck injury but did not describe the attack. He said police were looking into the reports involving the prom rejection.
"Whether or not that's rumor, or whether or not that's fact, we don't know," Mello said. "So I think it's important that no one ... speculate on these rumors. Those are things we're looking into.
"This is something that everybody wants to get to the bottom of and find out why it happened, how it happened and what can we do to make sure it doesn't happen again," he said.
Mello said town schools are very safe, despite not having metal detectors. He said police will be reviewing surveillance camera footage for evidence.
Janet Golden, Sarah and Rebecca's mother and a Milford alderman, said she rushed to the school to get her daughters. She said the stabbing most likely will result in more community discussions about school security, like those that were spurred by the mass shooting at Sandy Hook Elementary School in Newtown in December 2012.
"How can we create an environment that's safe for our children?" Janet Golden asked. "My daughter actually saw the victim lying on the floor, so I'm dealing with kids that are pretty traumatized now. I can't believe this is happening in our town. It's frightening."
A moment of silence was observed in Connecticut's House of Representatives for Sanchez, and students and town officials say her death was devastating to the community.
"This is a terrible day here in Milford," said state Sen. Gayle Slossberg, who represents Milford.