Police and rescue workers arrived on the scene, medical staff hurried to save the victims, and counselors helped students cope with the tragedy.
But an unlikely hero - a pro football player - was also rushing to comfort the shooting victims and their families.
And it's not the first time he's helped out in a big way.
A Heartfelt Gift
Representatives for Houston Texans' player J.J. Watt were on the phone with shooting victims and their family members just hours after the attack.
Family members say that the star defensive end offered to pay for any funeral costs connected to the tragedy. Watt also visited survivors of the shooting this week.
While originally from Wisconsin, Watt has a history of supporting his adopted city of Houston through troubled times.
In the aftermath of Hurricane Harvey, Watt set up a YouCaring fundraiser, hoping to collect $200,000 for relief efforts.
In less than two weeks, he collected more than $37 million.
A Player Who Cares
Watt's spirit of giving has earned him recognition from other celebrities, like Ellen DeGeneres, and from the NFL.
He was honored with the league's Walter Payton Man of the Year award for charity work in 2017.
While his high-profile donations have attracted a lot of attention, the Texans say Watt is even more caring behind the scenes.
The team says Watt always finds a way to help local cancer patients and people who have lost loved ones, even if he donates anonymously.
"People would be shocked if they knew how much he did privately," a team official told the New York Times.
As Watt says, "If you have the power to make someone happy, do it. The world needs more of that."
An Innocent Victim
One of the 10 students who lost their lives in the shooting was 17-year-old Sabika Sheikh.
Sheikh, a Pakistani exchange student, was set to return to her home country in just two weeks to celebrate Ramadan with her family.
Her host family, who have lived with her since she arrived in Santa Fe last August, say Sheikh was a bright girl who dreamed of becoming a diplomat.
Less than a week before she was killed, Sheikh had given her host mother, Joleen Cogburn, a handmade prayer shawl for Mother's Day. Cogburn wore the shawl at Sheikh's funeral.
"She was the most amazing person I’ve ever met"
While Sheikh's family could not be at her memorial ceremony in Santa Fe, more than 2,000 friends and strangers packed into a local mosque to celebrate her life.
Sylvester Turner, the mayor of Houston, said that Sheikh will "continue to be a diplomat."
"Because even in her death, she's building relationships between Pakistan and the United States."
Sheikh's host sister, Jaelyn Cogburn, teared up as she remembered the girl she called her best friend.
"She loved her family and she couldn’t wait to see them," she said. "And she loved us. She was the most amazing person I’ve ever met, and I will always miss her."
A Silver Lining
While so many young lives were cut short in the attack, many are choosing to remember the shooting's oldest victim, substitute teacher Cynthia Tisdale.
For the last two years, Tisdale worked two jobs to help support her husband, William, who suffers from a life-threatening lung condition.
By day she taught students, and by night Tisdale worked as a server in a local restaurant. All the while, she acted as a caretaker for her husband.
Tisdale's family set up a GoFundMe account a month ago to pay for William's treatment, but only received a few donations before Cynthia's death.
Now, the fundraiser is nearly complete, with new donations pouring in every minute.
"We don't know how to put it all into words but thank you doesn't give it enough justification," the family wrote in an emotional update.
"We (reached) the goal for funeral costs, bills, and possible lung transplant with second (doctor) that we never thought was an option."