Ten years on, the world-changing events of September 11 are seared in the collective memory - but to a whole generation of schoolchildren it is "ancient history".
Now a major education project for schools aims to help pupils understand the shocking sequence of events that day and grasp their significance in the wider world.
Research by the Institute of Education shows many of today's teenagers know little or nothing about what happened in New York and Washington in 2001, and teachers are afraid to cover the sensitive subject in lessons in case it stirs up racism. In response, academics have designed a programme for teachers who want to use the anniversary to tackle the issues head on.
Monday sees the launch of a web-based resource packed with interactive materials, suggested lesson plans and structured enquiries specially created by a team at the IoE for secondary school teachers to apply in their classes.
"If you talk to children they have very confused ideas about what actually happened and the sequence of events," Chris Husbands, director of the Institute, told The TES.
"For those of us who are adults, we think of it as very recent. We remember where we were and our reactions to it, and it had an enormous impact on how the world has developed. For young people this is almost ancient history. It's a lifetime ago for some children.
"Although there's clearly room for debate and disagreement, it's a formative experience in the making of the 21st century world into which children are growing.
"The consequences and the questions it poses around tolerance, multiculturalism and the nature of modern society are incredibly profound. There are a whole series of needs we are trying to meet with this programme."
Professor Husbands said teachers are overwhelmingly keen to tackle 911 in lessons but have told researchers they need help about the best way to approach it.
For some pupils, media coverage of the anniversary will be the first time they have seen images of the attacks.
Professor Husbands said it was also vital that pupils explore the background and consequences of 911 and that it must not be seen in isolation.
"The core of it is: what happened, why did it happen, why is it important?", he said. "We've provided a set of very clear structured enquiries into the issues around 911 in five subject areas - history, English, citizenship, art and drama.
"Some of them are incredibly imaginative. One that I think is really interesting is: when did 911 begin? That allows students to put it into a whole series of political and diplomatic developments pretty much over the course of the 20th century. Also interesting are some of the art enquiries about how experiences are memorialised, which gets into some very complex issues."
The programme, aimed at 11-to-16-year-olds, is backed by 911 Project London, an educational charity set up to help spread awareness of September 11 and promote cultural understanding. All the materials will be available free online from September 5. See http:9- 11educationprogramme.co.uk
911: Racism fears
Research released by the Institute of Education earlier this year reported that teachers were concerned about covering the 911 attacks for fear of sparking Islamophobia.
Heads of citizenship and PSHE said they had serious concerns about untrained staff taking lessons on the topic, saying it could have a "disastrous impact".
Original headline: A decade on, project aims to explain the events of 911 to the teenagers of 2011