By now, most US public school students have learned to barricade their classroom doors, turn off the lights, and hide in a closet if a shooter bursts into their school.

These mass shooting drills, also known as lockdown drills, are the sad reality of living in a country where kids are more likely to die in a school shooting than a school fire. That reality became jarringly clear Wednesday when one parent toured her 5-year-old daughter’s future kindergarten near Boston and noticed a disturbing nursery rhyme taped to the chalkboard.

It was an eerie twist on “Twinkle, Twinkle, Little Star,” reminding kids how to hide from a shooter during a lockdown.

Lockdown, Lockdown

Lock the door

Shut the lights off

Say no more

Go behind the desk and hide

Wait until it’s safe inside

Lockdown, Lockdown

It’s all done

Now it’s time to have some fun!

The parent, Georgy Cohen, was disturbed by the nursery rhyme and posted a photo of it on Twitter:

This should not be hanging in my soon-to-be-kindergartener’s classroom. pic.twitter.com/mWiJVdddpH — Georgy Cohen (@radiofreegeorgy) June 6, 2018

The tweet went viral, striking a chord with thousands of parents across the country whose own kids know these lockdown drills all too well.

I DO NOT want to see this as my son enters kindergarten in August! This cannot be real. — KellyStaples (@Kelly_Staples) June 7, 2018

School shooting drills are the new normal

The political stalemate over gun control has led schools to find creative ways to protect kids from gun violence. The most common response has been the mass shooting drill.

Since the shooting at Columbine High School in 1999, 32 states have passed laws requiring schools to conduct lockdown drills or some form of emergency drill to keep students safe from intruders. Some states went even further after 20 children died in Newtown, Connecticut, in 2012. Now six states require specific “active shooter” drills each year. That means the training must be specifically tailored to respond to an armed shooter. There is no consensus on what these drills should look like, but several states, including Missouri, require shooting simulations with police officers.

These mass shooting drills have become normal, and a generation of American students have learned to lock and barricade their classroom doors the same way they learn to drop and roll in case of a fire. Nine in 10 public schools now train students and teachers to respond to a shooter on campus, according to the National Center for Education Statistics.

The February 14 mass shooting at Marjory Stoneman Douglas High School in Parkland, Florida, led to another push for shooting drills.

Lawmakers in Florida passed a law requiring schools to conduct mass shooting drills twice a year, and lawmakers in New York and South Carolina introduced bills with similar requirements.