A shocking new advert warns families about the persistent threat of school shootings across the United States, with a back-to-school advertisement that takes a disturbing and sadly realistic turn.

The ad, titled “Back-To-School Essentials” and created by the school safety advocacy group Sandy Hook Promise, opens with a series of clips showing young students back in school after the summer vacation, showing off their new gear as if it were a commercial for a major retail outlet.

There are some warnings signs of impending trouble in the beginning — a teacher can be seen in the background of one student as she hurriedly closes the classroom door — but the message of the ad becomes more clear as a boy shows off his new headphones during an apparent shooting.

“These headphones are just what I need for studying,” he says in a library, before putting them on and looking down at a book. As he reads, other students can be heard screaming and seen running behind him towards an exit. The ad cuts to another boy running through a hallway as gunshots are heard and students are seen fleeing for their lives.

“These new sneakers are just what I needed for the new year,” the boy says as he runs away from the shooting.

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The ad was designed to be shocking, according to Sandy Hook Promise, a non-profit group founded by parents of children who were killed in the Sandy Hook shooting, in which a gunman killed 20 children and six adult staff members of a Connecticut school in 2012.

"It's meant to be an intense video," Nicole Hockley, the organisation’s managing director whose 6-year-old son Dylan was killed in the shooting, told CNN on Wednesday. The network has provided Sandy Hook Promise free air-time to showcase the public service announcement (PSA).

“This is what our kids are experiencing now in school,” she added. “We wanted to focus on this back-to-school time because parents still think of it as this rosy time where you're getting your staplers, shoes, folders and binders … Whereas, it's back to a time of violence for a lot of kids.”

The PSA arrived amid a rise in recent years of school shooting nationwide. Last year was reportedly the worst year on record for deadly gun violence in US schools since at least 1970.

Students across the country have since staged nationwide walkouts in protest of what they describe to be a lack of gun control legislation in the wake of frequent mass shootings.

The March For Our Lives saw historic crowds in cities like Washington and New York, for example, after it was led by students who survived the shooting at Marjory Stoneman Douglas High School in Parkland, Florida, where 17 people were killed and 17 others injured.

Ms Hockley said she believed the conversation surrounding gun control in the US has finally taken a turn of its own, and that she has not given up hope on Washington passing common sense gun reforms.

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"I think each time, sadly, we are moving closer to the time that it's going to be different (after a shooting). A lot has changed since Sandy Hook," she said. “The recent back-to-back shootings are so heartbreaking. The conversation continues to happen. More people are getting involved. Legislation is available in Congress right now that can start to chip away at these acts of violence. Prevention, plus legislation, that's the cure to this."