"This is a time for our country to take a look in the mirror and realize there is a serious issue here," David Hogg said on Good Morning America.
Hogg was at the school when the shooting started and hid in a classroom. He said that the school had done safety training recently, and he believes that saved hundreds of lives.
He said all of his friends are OK, but his younger sister lost two best friends.
"What I wish people would know is that, this is something that we cannot get used to," he said. "This is something that we can't let keep happening. Because if we do, and if we get used to it, it's going to happen again."