Faculty and staff greet police officers stationed outside of at Marjory Stoneman Douglas High School on Wednesday, Feb. 28, 2018 in Parkland, Fla. With a heavy police presence, classes resumed for the first time since several students and teachers were killed by a former student on Feb. 14. (Matias J. Ocner/Miami Herald via AP)

PARKLAND, Fla. - Like many teens, Casey Sherman was up late the night before, and was running a bit behind for her first day back to Marjory Stoneman Douglas High School. She scrambled to find her car keys in a bedroom with pale pink walls, clothes strewn across the floor and her hot pink bedsheets unmade.

She was in AP Spanish when the shooting at her school started Feb. 14, frantically calling her mom and staying on the phone with her older sister throughout the ordeal. She returned to the same class first thing Wednesday morning.

"It's important to start with fourth period to get it over with," said Sherman, who wore ripped jeans and a black lace-up sweater.

The 17-year old junior says she's not afraid to go back to school.

"I'm just nervous. I think it's going to bring back a lot of emotions," Sherman said.

"Oh wow, that's a lot of police cars," she said as she pulled into the student parking lot to meet her boyfriend. Officers and therapy dogs lined the streets. Students wrote messages of hope and solidarity on their car windows such as "Fly High" and "MSD Strong."

Volunteers handed out cookies and brownies as they helped students cross the street into the building.

Sherman had lacrosse after school. But the teen, who travelled to the state capital of Tallahassee last week to pressure lawmakers to support gun control, planned to spend the rest of the afternoon and evening helping to organize a march to Washington that has already received more than $2.7 million in donations.

"There's still so much to do. We've barely even broken the surface of it," she said.

That work has been a welcome distraction from the tragedy. She gives herself little time to think about it, instead working late into the night on reform and fielding calls and emails.

She sounds very business-like, with little hint of emotion in her voice. She's on a mission, with work to do and laws to change.

Her mother, Monica Sherman, hugged her daughter goodbye in the parking lot and the teen rushed along with her boyfriend.

Back to school, with everything changed.

"They're all adults now," the elder Sherman said. "Their childhood ended February 14."

News from © The Associated Press, 2018