The Lebanon Middle School dismissed early on Monday because of a hazmat issue.
The superintendent's office confirmed the early dismissal.
Officials said a container of solvent used to clean the school's septic system leaked in a custodian area.
They said there was a strong odor and the chemical can cause eye and throat irritation.
The school is located on Exeter Road.
Students were led to nearby Lyman Memorial High School and dismissed at 9:15 a.m.
Officials did not anticipate the school being closed on Tuesday.
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