Going back to school means worrying about what to wear, deciding what classes to take and, increasingly, knowing what to do if someone appears on campus with a gun.

This reality in American classrooms is reflected in a harrowing ad released on Wednesday by Sandy Hook Promise, a gun safety advocacy group created after the shooting at Sandy Hook Elementary School in Newtown, Connecticut, in 2012.

The spot, which debuted during the Today show, starts as cheerfully as any other back-to-school commercial, with a boy at his locker praising his new backpack.

Then, the testimonials darken. “These new sneakers are just what I needed for the new year,” one boy says as he sprints away from the sounds of screams and gunshots.

“These new socks, they can be a real lifesaver,” a girl says, peeling off her knee-high hosiery to use as a tourniquet on another student’s bloody leg.

In the final scene, a girl huddles in a bathroom stall and types out a loving text to her mother on a glittery pink phone. Tears stream down her face.

“I finally got my own phone to stay in touch with my mom,” she says, closing her eyes at the sound of a door opening and footsteps approaching.

“Gun violence and school shootings are not easy subjects, and they shouldn’t be fun to watch,” said Nicole Hockley, a former marketing consultant who co-founded Sandy Hook Promise after her six-year-old son Dylan died in the Newtown shooting.

“The more we step away from reality, the less respect we’re giving to those who have to live through this.”

Since the Sandy Hook shooting, more than 400 people have been shot on campuses around the country.

For many students, the excitement of returning to school is increasingly mixed with the anxiety of active shooter drills and shelter-in-place tutorials.

In response, gun safety activists are escalating their efforts. They are investing more in ads, promoting them more aggressively and making them far more provocative and uncomfortable to view.

Guns have long been at the centre of a divisive national conversation about public safety, personal freedom, partisan policymaking and corporate action.

In August alone, 53 people died in mass shootings, including shoppers at a Walmart in El Paso, Texas, and revellers in an entertainment district in Dayton, Ohio.

This month, Walmart said it would stop selling certain kinds of ammunition, discourage customers from openly carrying guns in its stores and encourage debate around gun reform legislation.

Last week, the heads of nearly 150 companies, including Twitter and Uber, sent a letter to Senate leaders calling for stronger background checks on firearms sales and “red flag” laws.

In a blog post last month, the online firearms retailer K-Var wrote it had been notified NASCAR was shifting its position on guns and had demanded that ads featuring firearms be changed before they would be included in its official racing programs.

The racing organisation did not respond to a request for comment.

-with New York Times