The Kluckholn Elementary School in Le Mars was evacuated over the lunch hour Thursday after complaints of an odor in the building.
Le Mars firefighters and crews from Mid-American Energy were called in to investigate for a possible natural gas leak.
Firefighters used special monitors to thoroughly check the building, but Le Mars Fire Chief Dave Schipper says nothing unusual was found.
The origin of the odor was not determined and the monitors all indicated a zero presence of natural gas in and around the school building.
Firefighters were on the scene for just over an hour and then students returned to their classes.