Fife School District Assistant Superintendent Jeff Short said the bus was on its way to Surprise Lake Middle School when the substitute driver became incapacitated.
Seventh grader Jeremy Wuitschick was on the bus and said the driver let go of the wheel and started flailing his arms.
"I knew something was wrong," he said.
Wuitschick said he got up and grabbed the wheel, turned the bus toward the side of the road and turned off the ignition.
"It was pretty scary," Wuitschick said. "It was all happening really quickly."
Video from a security camera aboard the bus shows another student helping Wuitschick with the wheel as the bus came to a stop outside of Discovery Primary School, which is adjacent to Surprise Lake Middle School.
John McCrossin, director of student programs for the Fife School District, was driving behind the bus when he noticed the bus veer off to the side of the road.
He ran onto the bus after it stopped and found the driver unconscious and not breathing. The kids told McCrossin they already called 911, so he began performing CPR on the driver until police and medics arrived.
The driver was taken to a hospital, but his current condition was not known. Police originally said the driver suffered a heart attack, but hospital officials have not yet confirmed what caused the driver to lose consciousness.
Fife Police Chief Brad Blackburn said no one else was hurt thanks to the students who brought the bus to a safe stop.
Watch: Jeremy Wuitschick describes what happened:
Watch: Bus surveillance video of incident