The attack on Sandy Hook Elementary Shoot remains the deadliest mass shooting at a American school.
A total of 26 people - including 20 children aged six and seven - when a gunman stormed the campus in Newtown, Connecticut in 2012.
The incident sparked fresh debate about US gun control laws and now Sandy Hook Promise (SHP) - a group made up of some of the families of the victims - has released a 'public service announcement' (PSA) video to raise awareness about the issue.
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The footage starts like a normal back-to-school commercial with youngsters discussing new rucksacks, folders and gadgets.
But the video takes a frightening turn when the sound of gunfire and screams are heard. The children use their back-to-school items to try to save themselves and their friends from an unseen gunman.
One girl uses school socks to stop the bleeding of a stricken classmate. In the most difficult to watch scene, another girl is shown hiding in a bathroom texting her mother a "I love you mom" message on her new phone.
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SHP co-founder Mark Barden said: “This PSA is a gut punch, it’s uncomfortable, it’s hard to watch, but you can’t sanitise a school shooting. My hope is that folks will see this and be inspired to take action.”
Mr Barden's seven-year-old son Daniel was one of the casualties of the shooting in December 2012.
The video is part of SHP's 'Know the Signs' campaign which seeks to prevent school shootings and suicides by identifying students at risk of hurting themselves or someone else.