People who know Sef Scott know he doesn’t normally speak. The 17-year-old has autism, and other than quoting lines from favorite movies, he is mostly nonverbal.

So the members of the Plano (Texas) Senior High School Class of 2018 — along with Sef’s relatives and even his father — were stunned when he took the mic and addressed his fellow graduates.

“I would imagine that to the seniors that know who I am that it is entirely unexpected that I would be standing here giving a speech,” he said. “Just by my being here speaking to all of you — me — that alone is unexpected. Knowing that I want to be heard — I imagine that is unexpected.”

While many students had seen Sef in the halls, he was largely in special-needs classes and most didn’t know him, said his mother, Vicki Scott. She doesn’t know quite why, but when she saw a notice inviting seniors to audition a speech for graduation, she had an inkling that he’d want to do it.

She ran the idea by him, and he said, “Yes!” His response took even his mother by surprise. “He’s not a demonstrative individual at all, and to have him shaking with excitement, with a huge smile, making eye contact, looking at me straight in the eye and firmly saying yes, it was great.”

The speech took seven weeks of writing and editing, helped by his brother Sim, 15, who has given many speeches about having had a brain tumor.

When Sef started elementary school, his parents worried he’d be a target for bullying. Instead, they saw his classmates holding his hand and leading him to where he needed to go. They decided that they could never move away from the place where other kids knew him and cared for him.

But to get onto the graduation-day podium, Sef had to audition before a panel of judges who did not know him. His mother and brother did not tell anyone else about the plan, and his father and other relatives had no idea it was coming.

As they sat in the audience, Sef stepped up to the podium.

“Unexpected,” he began. “This is what I want you to remember. Unexpected.”

He also told graduates to follow their own hopes and goals and not just blindly tread a path that doesn’t feel true to them. “Don’t follow someone else’s dreams. Don’t waste time on something you never wanted. Do the unexpected. It’s your life that you are living, not anyone else’s, so do what fulfills you. Don’t fear the future, don’t fear the unknown. Will it be unexpected? Yes. Yes it will. But that does not make it wrong.”

At a couple of points, the audience burst into applause. Then Scott began hearing sniffling around her. Then she started sniffling.

Sef got a standing ovation.

The theme of his speech applied to everyone in the room, special needs or not, said Brittney Love, a paraprofessional at the school. “Do what’s best for you — I think that’s just perfect,” she said.

Sef’s mother thinks his willingness to speak was driven by a realization that this was the last opportunity he would have to be with the schoolmates he’d grown up with, and he wanted them to know him.

She said, “It makes me think that in recent years, maybe he wanted to all along.”