"As soon as the teacher suspected a funny smell we got the students out and put them in the hall so no one was exposed to the toxic smell all day."
The school was evacuated within about an hour and 13 students, two teachers and a parent were taken to Hawke's Bay Hospital as a precaution.
Ms Smith said they were all discharged on Monday night.
Liquid mercury is not readily absorbed through skin but vaporises at room temperature and inhaling the vapour can be harmful.
Symptoms of exposure to the neurotoxin include tremors, insomnia, neuromuscular changes and headaches.
Fire crews and a hazardous materials team decontaminated the affected area on Monday afternoon ventilating the affected classroom and removing the carpet.