A special education teacher who detailed her experience administering a lockdown drill in a now-viral Facebook post described to ABC News how nerve-wracking it was to practice the drill with a room full of elementary students with learning disabilities.

Dana Williams, who teaches at an elementary school in Pittsburgh's Hill District, described the experience as "scary," but also marveled at how well her young students handled the ordeal.

The drill -- the first of the school year -- was planned in advance, Williams said. Letters were sent to students and parents detailing the exact date and time of the drill, and a robocall was placed to all of the parents.

But even though "everyone knew this was happening," Williams said the drill wasn't "at the top" of her students' minds.

Williams decided to teach right up until the 9:30 a.m. drill time. At the time, the students -- ranging in age from 7 to 10 years old -- were taking their district assessments. Williams and her teaching assistant were providing support.

Then, the principal's voice came over the intercom to announce the lockdown, and she and her students sprang into action.

The only fifth-grader in the room, a 10-year-old whom Williams has been teaching since kindergarten, "took a lead role" and immediately went over to the windows to pull down the blinds, she said. She locked the classroom door while her assistant pulled a table in front of it.

The assistant then pulled two students under her desk, located across the room. Several other students went underneath another table, located as far away from the door as possible, and the fifth-grader grabbed a second-grader and pulled him underneath as well, Williams said.

Once Williams turned off the lights, her normally rowdy students became "literally casket quiet," she said. Then, one of the iPads the students were working with went off, and a third-grader grabbed it and turned it off before she could get to it.

Williams said it was obvious how "panicked" her students were when someone came to the classroom door, jiggling the handle and ordering them to "open up."

"You could see it in their faces," she said.

The youngest in the room, a first-grader wearing a birthday crown because he turned 7 that day, dashed to her, quietly whispering, "I'm scared." He asked "over and over again" when the drill would end.

She told him "soon" and held him while trying to keep his crown from stabbing her, she said, adding it felt as if his heart had "leaped out of his chest."

"It was dark. I couldn't see anything," she said. "I just saw eyes. One of my students was crying."

After the drill was over, Williams turned on the lights, announcing to her students, "Let's get back to work," considering all of the testing they had left to complete.

"I was greeted with blank faces ... petrified faces ... tear-stained faces ... confused faces ... elated faces ... and one 'b---- REALLY?' face," she wrote on Facebook.

Instead, the class partook in some mindfulness and restorative exercises to transition to the start of the rest of the day, she said.

Williams said she was "amazed" at how well she, her teaching assistant and her students adapted to the drill.

"It was kind of amazing to see kids that young robotically do and know what they were supposed to do, without even a discussion, nothing, Williams said.

Williams, 38, said this has only been the third or fourth lockdown drill she's practiced in her 17-year teaching career. Despite how "scary and traumatizing" the most recent one was, she thinks they're necessary.

"With our current climate, there's so many shootings," she said. "It's all over the news. It's all that you see, and I'm a big proponent of being prepared. I'd rather be proactive than reactive."

Officials for the school district confirmed that the drill took place last week, adding that teachers are instructed to not unlock the door "for any purpose" once it is locked. Administrators were tasked with going from classroom door-to-door to ensure the door was locked, one official said.

Williams teaches in an urban, inner-city setting where shootings are a part of everyday life for a lot of her students, she said. She has had students who were shot at and students "who walk through gunfire to get to school," she said. Some students have even been shot themselves, and some have had parents who were shot and killed or severely injured, she said.

In addition, some students don't know where their next meal is coming from, and some as young as 10 are caring for younger siblings, she said.

She stressed the need for more counselors in schools "so students can sift and talk through these feelings."

"Unfortunately, most of the mental health is the teachers," she said.

The Facebook post Williams composed on the day of the drill garnered nearly 90,000 reactions and more than 80,000 shares as of Wednesday night.

She didn't expect her post to get so much attention, she said.

"This is my life as a teacher," she said. "Not only do I have to do active shooter drills, I do assessments. I need to calm students down, and I have to instruct them."

"There's a lot of things that teachers have to deal with," Williams concluded.