Colleen Billings was just settling into first grade when the world changed.
"I remember my principal coming on the announcements and everyone was really quiet," Billings recalls of that day in 2001. "and it was my best friend's birthday, and we all thought we were getting out of school because it was her birthday.
"My mom's best friend picked me up. She brought us back to her house, and we were playing around, and my brother, who's older than me, said 'Do you understand why we're all out of school?' And I said no, not really."
Billings is now a senior at Hendrick Hudson High School in Montrose. Her classmates relate similar impressions of a historic event they did not understand at the time. Most of what the senior class knows about Sept. 11, 2001 came from teachers.
More and more, as years go by, the event is history, related in books and classroom lessons.
"I took AP U.S. history and it came up," senior Ed Tandy said. "It's in the newer textbooks now, too. Everybody was young. I don't really remember too much. But it comes up in class. And of course on 9/11 we have the moment of silence in school that comes over the announcements."
Teachers are still figuring out what to say about the event. Those who lived through it are struck by the emotional distance they see in students.
"For them, it's as if they're seeing a movie," said John Annunziata, a social studies teacher at Hendrick Hudson. "Some of them might have personal anecdotes. But what I see, especially now, eleven years out, is that there's no emotional connection for them whatsoever. I mean none."
Frequently, the attacks are covered as part of a larger discussion of terrorism.
"When we talk about terrorism, it's not just a specific event," said Richard Zangrilli, who teaches U.S. history at Hendrick Hudson. "It's like when you talk about World War II, you talk about the Holocaust, and you talk about some major battles."
Inevitably, written materials are supplemented by the personal recollections of teachers.
"I wouldn't say I squeeze it into the content," said Annunziata, who was teaching in Yonkers that day. "But I bring it up because I want to see if they want to talk about it or if they want me to share any anecdotes from being a New Yorker who was near the city on that day."
While some teachers would prefer to spend more time on the topic, their options are often limited.
"I can't say a lot because very often we are bound by a curriculum that we have to get from point A to point Z in a certain period of time," Zangrilli said.
Organizations such as the 9/11 Memorial and the Morningside Center for Teaching Social Responsibility have put together complete lesson plans on that day. The 9/11 Memorial organization has tied their lesson plan to New York State's Common Core Learning Standards, the guiding curriculum standard for all schools in the state. The lesson plans offer educators options beyond the sober facts of who, what, when and where.
One of the issues teachers focus on is who was responsible, and more importantly, who wasn't.
"I think one of the main lessons is that it's not about being a Muslim. It's about being a terrorist," said Hendrick Hudson senior Eva Baransky. "It's about having a crazy hate for something, an obsessive hate for something. And that we shouldn't persecute people just because they are Muslim or they have a certain belief system. That's very stressed in class."
When Annunziata covers terrorism and the modern jihadist movement, he starts with what he views as its genesis, the Iranian revolution of 1979. Next, he delves into the Soviet occupation of Afghanistan in the 1980s, and from there, how the movement spread to become what he calls a "war without borders."
"I go out of my way to stress that first of all, the vast majority of Muslims are not even Arab and the vast majority of Muslims are people who live in economically challenged societies and are just trying to feed their kids," Annunziata said. "Not just to be politically correct, but to be historically correct.
"I remind them that it's not over. These people are very methodical and they took a long time to plan 9/11 and we weren't watching them. Now we're listening and we're watching. They're still out there. What I try to do is stress that they are a fringe element."
For teachers who were in or near New York on Sept. 11, the subject remains intensely emotional. The students pick up on that.
"You can just tell on their faces," said Hendrick Hudson senior Bailey Stewart. "They went through it, they experienced the whole thing as it happened. You can tell it's a deep thing to them."
Students and teachers agree that the events of Sept. 11 warrant discussion in the classroom, despite the raw emotions the discussion may evoke.
"We'll watch that video every year in class," Billings says. "And everybody has goose bumps, no matter what,"
"I think it's important that people know and see," agrees Tandy. "Even though it's very hard to watch, it's important to see what happened."
Looking toward the future, Baransky thought about how she would want to broach the subject with her own children.
"I will probably tell my kids about it in a very factual way," she says. "And then I'll probably open up to them emotionally in how I think we didn't just take a hit as New Yorkers, we took a hit as a country."
Morningside Center for Teaching Social Responsibility -- 9/11 Anniversary Teaching Guide (created for 10th anniversary):
9/11 Memorial lesson plans: