Evergreen Public Schools says it had been investigating the ride that one busload of Silver Star Elementary students took on May 14. On Wednesday, the district said the driver had resigned and the investigation was complete.
Angry parents had flooded the district with phone calls, saying children were forced to ride with the windows closed while temperatures climbed into the 90s.
Parent Jamie Boyce says her son was beet red and drenched in sweat when he got home.
District spokeswoman Gail Spolar says the driver had 25 years with the district. The driver was not identified.
School district rules say the driver must set windows at an appropriate level before children enter a bus.
The district says it has reminded drivers of proper procedures to ventilate a bus on a warm day.