It was about three years ago, the first time Jerry Swiatek got to the 9/11 portion of his social studies class and had some freshmen say they'd never seen footage of planes flying into the World Trade Center.
Each year since, more students among the current crop of 15-year-olds tell him the same thing, leaving him still amazed that they've never experienced the horror of watching the twin towers collapse.
It's etched forever in the minds of their teachers, but for the majority of school children, Sept. 11, 2001, is a day of infamy they don't remember.
This year's high school seniors were in second grade a decade ago. Their memories of the day of the attacks are fuzzy at best _ a teacher crying while hugging a colleague or being shepherded into the auditorium away from televisions filled with scenes of horror. For younger kids, it's an even more distant event.
"They've heard about it, they are aware of changes that have taken place in our country, but their parents have never let them see the footage," said Swiatek, who teaches mostly high school freshmen in rural Citrus County, Fla., and shows news clips of the burning towers to shocked students each year around Sept. 11. "Students who had never seen it couldn't believe what they were seeing. I was a little concerned."
More than 60 million children in America are 14 and younger, according to the U.S. Census Bureau. So how do teachers handle the daunting task of trying to explain the significance of 9/11 to students who don't remember when anyone could walk right up to the gate at the airport or when Osama bin Laden wasn't a household name?
The answer isn't simple, and it has changed over time as the country's rhetoric about the attacks has evolved.
Students across the country will gather for assemblies, hold moments of silence and spend history and social studies classes focusing on Sept. 11 this year. They'll hear stories from teachers and talk to survivors or family members of victims.
They'll read front-page headlines screaming "UNTHINKABLE" or "ACT OF WAR" in giant letters.
Though it's been a decade, just a few states and school districts have a set curriculum for teaching Sept. 11. Unlike Pearl Harbor or the assassinations of the Rev. Martin Luther King Jr. and President John F. Kennedy, the story of 9/11 is still being written as the country continues to grapple with its impact.
New Jersey unveiled its new curriculum this year in honor of the 10th anniversary of the attacks, a lesson plan created by families of Sept. 11 victims and the New Jersey Commission on Holocaust Education. It provides 56 lessons _ which start simple and grow in complexity and maturity with each grade level _ emphasizing the good that came out of the tragedy for younger students and examining the history of terrorism and other complicated lessons for older students.
The lessons recommend some kind of action, such as creating art about tolerance or service projects to honor or remember victims.
"We really wanted something broader in scope, that Sept. 11 would have a context to it," said Donna Gaffney, a co-founder of the 4 Action Initiative, which put the materials together.
In 2009, New York City schools piloted what was believed to be the first comprehensive educational plan focusing on the attacks. Created by the New Jersey-based Sept. 11 Education Trust, the curriculum has also been tested in schools in California, Alabama, Indiana, Illinois and Kansas. It uses videos and interviews about the attacks, as well as interactive exercises like having students map global terrorist activity with Google Earth software.
New York City, the nation's largest school district, announced an updated Sept. 11 curriculum this month that includes tips on how to help students cope with learning about the horrors of that day, a study of the art inspired by the terrorist attacks and a history of the building of the 9/11 memorial. The project was done in partnership with the National September 11 Memorial & Museum and a group of New York City educators.
A few nonprofit groups _ like the Sept. 11 Education Trust founded by Anthony Gardner, whose 30-year-old brother, Harvey, died in the World Trade Center _ have come out with lesson plans but those programs have not become widely adopted. Even the U.S. State Department has developed materials for educators.
"It's a long process to get the program out there in the hands of teachers and making teachers feel equipped to handle it with students," said Gardner, who said his curriculum is used at least in part in about 2,000 schools across the globe. "Maybe by the 25th anniversary there will be programs in place that meet the need."
For the most part, states and school districts leave it up to the teacher, which can mean some students don't hear about it at all. Some teachers may avoid the subject altogether, either because they are concerned about how younger students will take it or because they simply are too emotional to talk about it themselves, said Louisville, Ky., fifth-grade teacher Carla Kolodey. Other teachers said history classes often have difficulty getting to 1980, much less 2001, by the end of the school year.
Kolodey starts her lessons with a description of life before Sept. 11 and then warns her students that the content could be tough to sit through. She tells them they can leave the classroom if necessary, then shows them TV footage and newspaper clips of the attacks. She brings in speakers who lost a family member in the World Trade Center or who have other personal connections to the day.
"I've had kids in tears who have to step out and collect themselves," said Kolodey, 31, whose social studies textbook dedicates just one page to Sept. 11. "I've gotten emotional in the middle of it and said, `You need to understand that I might need a moment to collect my thoughts.'"
Macon, Ga., high school world history teacher Jason Williams said he tries to focus his lessons on religious tolerance. He said he starts the lesson asking students to talk about biggest news events they remember _ like the explosion of the space shuttle Columbia _ and tells them that Sept. 11 is that day for him and many other adults.
"They're very serious about it, but as the years go by, they're a little more dull to it because they didn't experience it firsthand," Williams said.
Though the topic is covered by nearly every history and social studies textbook on the market, researchers have found that the mentions are scant. Teachers can use online resources from newspapers or foundations to help supplement, but it's up to them to find that material.
Textbook companies, some of whom pulled social studies and history books from the presses just after the attacks and updated them to mention the events of that day, are releasing online lesson plans and other supplemental teaching material for educators.
The material in textbooks has changed over time, too, from stories about heroes to examinations of the wars in Iraq and Afghanistan, researchers at the University of Wisconsin found. The story of 9/11 and its effects is evolving, making it difficult to use the same lesson each year.
"The first few years things were a little bit more coordinated and there was a great deal of sensitivity. I think in the last five years we've gone through a period where it was a little bit more left to the individual teacher," said Eric Sundberg, who focuses on social studies curriculum for the Jericho School District outside New York City. "I expect on the anniversary coming up we're going to speak at length again as departments and as schools on how we want to address the issue."
Atlanta parent Leslie Grant, who has a daughter in seventh grade and son in third grade, didn't want to simply leave it up to her children's school to teach about such an important event. She sat them both down at the computer last year and showed them footage of the attacks, and found that she had trouble looking at the images as she explained what happened to her stunned children.
"I don't mind if they handle it straight-on," said Grant, who lived in New York City during the 1993 World Trade Center bombing. "We watched a video of when the planes hit, but I was unable to continue watching. We shut it down and talked about it."
In Shanksville, Pa., where United Flight 93 crashed in a field with a force so great it shook the school three miles away, the memories of 9/11 have never faded, even though textbooks there don't mention the attacks because they are about a decade old. Students at the school have marked the day by going to speeches at the crash site or hosting speakers such as former governors Ed Rendell or Tom Ridge, who held the office at the time of the attacks and became the first secretary of Homeland Security.
Thomas McInroy, who heads the tiny Shanksville-Stonycreek school district consisting of a single K-12 building with fewer than 400 students in western Pennsylvania, said his students, no matter their age, are "living it every day." Today's rising seniors were second-graders at the time, and their families comprise many of the local volunteers who responded to the crash and later staffed the temporary memorial at the site.
"Every time our kids wake and our parents wake up, they are reminded of it," McInroy said.
Associated Press writers Kathy Matheson in Philadelphia, Frank Eltman in Long Island, N.Y., and Geoff Mulvihill in Trenton, N.J., contributed to this report.