Shadow Lake Elementary School was evacuated shortly before 3:30 p.m. last Thursday when smoke was detected in classrooms, according to the Tahoma School District.

The district’s maintenance supervisor, Bob Schuler, said the source of the smoke in the Unit A portion of the school was cardboard packing material that ignited inside a heat pump when the pump motor overheated and failed. District maintenance workers located the problem and replaced the motor Thursday evening.

Classes resumed their regular schedule Friday.