By Multimedia Producer Elisa Menendez
Hundreds of teachers and students have shared their "traumatic" experiences of active shooter drills at US schools in the wake of the Uvalde massacre.
As the lives of 19 young children and their two heroic teachers are mourned, renewed calls for an urgent crackdown on gun control have swept across the country, while bereaved parents issued direct pleas to politicians to act and students staged class walk outs.
18-year-old Salvador Ramos' attack on Robb Elementary School, in the southwestern Texas town of Uvalde, led to an outpouring of Americans' chilling personal accounts of shooter drills, that often simulate real-life gun attacks.
The routine "lockdown" drills - intended to help teachers, school staff and students practice what they would do if there was a real shooter on campus - have become a "normalised" part of American children's school experiences, many say.
In a now viral tweet, Erin Hahn described how teachers are taught in training that if a student is outside of the classroom during a drill, they have to lock them outside.
"Even if they beg and bang on the door," she wrote: "Because there could be a shooter using them to access your classroom.
"I still have nightmares about having to do that."
Ms Hahn's tweet, which received tens of thousands of shares and comments, garnered stories from students who said they'd stopped using the toilet at school because they were "afraid" of being locked out during a drill, or worse, a real attack.
"I don't know that there are any teachers who know how to do it [the drill] without scaring kids because you want them to take it seriously because it could happen, but you also don't want to traumatise them," former teacher, Ms Hahn, added to ITV News.
"And that's a balance that we shouldn't even be asking our teachers to make."
Tea Kurbegovic, now 22, still remembers a frightening "code red" drill - a total lockdown - she participated in when she was about eight-years-old.
"While we were all huddled together in the dark, someone started banging on the door asking to be let in," she recounted.
"The teacher whispered to us, asking us what to do. I said let them in, and the teacher told me to go open the door.
"I opened it, and before I even recognised that it was my principal dressed in full black, she put two fingers to my head and said 'bang, you're dead'."
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Lockdown drills were introduced after the 1999 Columbine High School massacre, where 13 teenage students and a teacher were killed. They have dramatically increased following the 2012 Sandy Hook school shooting when a gunman fatally shot 20 children and six staff members.
The drills vary widely between school districts - often a staff member will play the role of the shooter moving door to door jiggling handles, while students are instructed to hide and remain as quiet as possible.
Some students are asked to play dead or injured and are smeared in fake blood, while a masked assailant carries a fake gun.
Teacher training drills without students are "much more intense", said Ms Hahn, adding: "They have police officers shooting blanks in hallways so we can get used to the sound."
Amid a political deadlock over renewed gun laws, American schools are paying over the odds into an estimated $3 billion (£2.38bn) education security industry for metal detectors, bulletproof glass, armoured doors, security guards, and resources to host lockdown drills.
An estimated 95% of American public schools now carry out such drills.
Robb Elementary is one of those schools. A teacher, who spent 35 minutes huddled on the floor with her pupils, said when they heard shooter Salvador Ramos' gunshots down the hall, they knew exactly what to do.
“They’ve been practicing for this day for years,” the unnamed teacher told NBC. “They knew this wasn’t a drill. We knew we had to be quiet or else we were going to give ourselves away.”
Uvalde High School, where Ramos was a student, also undertook an active shooter drill in March. It was overseen by UCISD police officers including Ruben Ruiz, whose wife fourth-grade teacher Eva Mireles, 44, was killed by Ramos in Tuesday's massacre.
Teachers are told not to share information about the lockdown drills because it could give a potential shooter "intel" into the school's systems and protocol, said Ms Hahn, who left the education sector in 2020.
"They already know what we're doing - the 'intel' we have - because they've faced it themselves," she said. "These kids [school shooters] have come up through the school system during the time that we've had these active shooter drills.
"There's no hiding from that anymore, we need to address it."
Everytown, a US gun violence prevention organisation, argues there is "almost no research affirming the value of these drills for preventing school shootings or protecting the school community when shootings do occur.
"Students, educators, and staff have experienced distress and sometimes lasting trauma as a result of active shooter drills."
A former teacher, who wished to remain unnamed, said she "hated" doing the "awful" drills - and they were one of the reasons she left teaching.
"I can’t tell you how it broke my heart to help crying kindergarteners who were locked out of their classrooms to find a bathroom to lock themselves in until I came to tell them it was safe. It was brutal," she said.
"They’d tell us to shake the doors as hard as possible and listen to see if kids reacted [or] screamed, so we could 'coach' them later on how to hide better."
Tea Kurbegovic, who was five-years-old the first time she took part in one, said: "Kids would cry every single time".
"We were left pretty shaken as a group and it only got worse as we got older because every year they increased the intensity of the drill," she told ITV News.
"Eventually, kids stopped crying, but after the drill the room would take on a much more somber tone. Like we're all sitting at our desks and reflecting on our own mortality.
"By the time I was 10 I also was more aware of the news and the fact that it seemed like every week another school was getting shot up in America. I was 12 when Sandy Hook happened. I was terrified."
When she was 16, someone did bring a gun onto campus.
The school didn't order a "code red" - only a partial lockdown where hallways were cleared and doors locked but classes continued as normal.
Thankfully, she says, the gun was never discharged.
"I don't know why they did that when there was a clearly highly distressed individual on campus with a gun," she said.
"Would we have to wait until someone actually gets hurt for it to be a code red? How far is the school willing to let things escalate before they consider the threat serious enough to warn us and have us take cover however we can?"
Despite the often upsetting nature of active shooter drills, some argue that until gun controls are tightened in the US, they are needed.
"As long as America values guns more than the lives of children, it's a necessary evil," said Ms Kurbegovic.
"If America won't address the issue of gun violence head on, we have to prepare kids because these tactics might actually save their lives, as horrible and traumatic they may be to learn."
Ms Hahn, who is from a family of hunters and owns guns herself, says guns "should not go away full stop" but at the very least, background checks must be introduced.
"There's definitely something systematically wrong with anyone being able to get their hands on these things - such high powered weapons that can do so much damage in such a short amount of time. There's no reason for that," she said.
Referencing the Sandy Hook shooting, she adds: "We're still fighting the same battles as we did 10 years ago - but now they're increasing the drills.
"That's not the right answer."