Most Americans remember exactly what they were doing and how they felt the day terrorists hijacked four airplanes and crashed them into the World Trade Center, the Pentagon, and a field in Pennsylvania.

But now, 25 years on from the 11 September 2001 attacks, there is a new generation, too young to remember the day that permanently altered much of American life.

Members of Generation Z, born between 1997 and 2012, were told - well after the fact - about the event that undoubtedly reshaped their futures.

They carry distinct memories not from the day itself, but from the moment years later that they learned about the attacks.

An adult and child laying flowers at the 9/11 Memorial on the 25th anniversary of the attacks

Avery Black, 20, a journalism student at the University of South Carolina, remembers hearing about 9/11 for the first time in elementary school, then going home and asking her mother about it, she told the BBC.

"She just started telling me where she was the day it happened, and just broke down in tears, explaining to me about all the firefighters that went in and never came out," Black recalled.

As a child, Black didn't quite grasp the day's gravity, but for her, certain details still stand out.

She remembers, most distinctly, the "falling man" – a famous image of a man plummeting, upside down, from the North Tower. A Dallas, Texas native, she also recalls teachers showing the video of then-President George W. Bush first learning about the attacks at an elementary school event.

For Annie Erickson, 26, who grew up in North Carolina, personal anecdotes, more than school or reports, created her first memories of 9/11.

"My mother grew up in New York City, so I remember my mom telling me about 9/11 and talking about how someone that lived in her building, who she was friends with, passed away in the towers," Erickson said.

She also was struck when learning about 9/11 at school that it was one of the few historical events teachers could personalise with their own memories.

Currently, there's no national requirement for US schools to teach students about the attacks, and the expectations vary widely by state. Twenty-five states require or expect public schools to teach the events of 9/11, while 13 make 9/11 instruction optional, according to a recent analysis by The Associated Press.

But not every state that requires it specifies a curriculum.

Allegra Tashjian, who grew up in Wisconsin, said her teacher explained in first or second grade that it was a very important, sombre day and asked if anyone knew why. After a student responded that it was the day planes hit the towers in New York, Tashjian wondered why she had never heard of it before.

Later, at home, she recalls finding her mom folding laundry and asking if she remembered planes crashing in New York. "I remember she kind of paused folding her laundry and was like, 'um no, I don't think I've ever heard anything about that,'" the now-28-year-old PhD student said.

"For whatever reason at that point, I guess she really didn't want to talk about it."

Tashjian, Erickson, Black and several other Gen Zs all told the BBC that they remember hearing a few details about the attacks in school and from their families, but only through their own research did they learn in depth what actually happened that day.

"I really understood the gravity of it more from reading things on the internet when I was probably between like nine and 12", Tashjian said.

Black didn't realise at first that it was a terrorist attack at all. "That was the part that I wasn't really taught until I did my own research. It's really hard to explain what a terrorist is to a child."

Professor David Schanzer, who teaches "9/11 & Its Aftermath" at Duke University, wrote this week in a campus magazine commentary that there's still strong interest generations later. His course is full, with dozens on a waitlist.

"Ten years ago, I thought student interest was ebbing and I would need to find something else to teach about," he said.

But current world events, he said, only made young people more curious about what happened 25 years ago on 9/11.

"If you want to understand what has gone wrong over the past couple of decades it makes sense to learn about 9/11, the first global catastrophe of the 21st century (the others being the Great Recession and the COVID-19 pandemic)," he wrote.

The downtown Manhattan skyline fills with smoke on 11 September 2001

Several Gen Zs told the BBC that, despite gaining knowledge about the tragicday, it is still common among peers to actively lighten conversations about 9/11.

Thomas Schwartz, a professor of history and political science at Vanderbilt University, said in a recent class discussion, his seniors - born in 2004 or 2005 - remarked on their generation's tendency to "deflect and joke about 9/11".

He added that "students from the Northeast, who had parents with personal memories of 9/11, were more careful about this, remarking on the sensitivities in their family about the subject."

Erickson said many Gen Zs tend to downplay monumental events or tragedies because either they "can't fully understand their impact" or they're using humour as a coping mechanism "to not have to think too deeply about some of the larger anxieties in our world".

Even now as an adult, Tashjian said it's still difficult for her to fathom large numbers of people dying in any event, and she still gravitates toward individual anecdotes to help her understand 9/11's toll.

Schanzer contends that learning about 9/11 and understanding its impact remains crucial for younger generations without first-hand knowledge.

"But like most significant historical events, one can't fully understand our world today unless you understand why 9/11 occurred and how the United States responded to it," he said.

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