Emmanuel Williams, 17, leapt into action to wake the dozing driver, averting potential disaster.
The dramatic moments were captured on the bus CCTV.
Emmanuel noticed the driver's head nodding strangely when the bus started swerving. He jumped from his seat and roused the sleeping man.
"I was looking at him and his eyes would close, and when we'd get to a turn, he'd look both ways, start driving again, and they would close more and more," said Emmanuel, a pupil at Mount Tahoma High School, Washington, U.S.
"And as soon as I see his head go down, and I see the bus go back to the freeway, I hop up, get to the front of the bus as fast as I can. Something would have happened if I didn't get up.
"I know that there would have been a big huge thing going on because he would have crashed and it would have been a whole lot more than what it is now."
School officials are looking at all possibilities for what might have caused the driver to fall asleep, including health conditions or medications.
Excellent work, Emmanuel.