Jeremy Wuitschick, 13, grabbed the steering wheel from the incapacitated driver and drove the vehicle safely onto the curb.
Wuitschick told KOMO News: "I knew something was bad because he looked like he was having a seizure and choking.
"I was just acting on instinct. It was all happening really quickly and it wasn't like the movie ones when they scream and stuff."
Praising the schoolboy's "quick-thinking", Bill Rhodes told ABC News: "He did the right thing and we're going to do something for him. The kid definitely deserves credit."
Before an ambulance could arrive, fellow student Johnny Wood successfully performed CPR on the male driver, who remains in "a grave condition" in hospital.
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Watch a news report showing footage of the incident below: