The Maria Sanchez School, at 176 Babcock St. in Hartford, was evacuated for about half an hour after an electrical problem caused an odor on Tuesday morning.
A security guard and a custodian have been taken to Hartford Hospital as a precaution because they felt ill.
Students said others started feeling sick, but did not need medical attention.
The Hartford Fire Department checked each room of the school with meters, but did not find anything hazardous.
Students were allowed back inside the school's gym to get warm after the building was checked.
Many concerned parents have since come by to pick up their children as the investigation into the source of the problem went on.