A classmate used profanity in class. He was required to chew on a piece of soap ("washing out the mouth with soap"). He was suspended from school for two weeks.
A schoolmate mischievously activated the school's fire alarm, which resulted in all of the students and teachers quickly leaving the building and assembling in the schoolyard. In the presence of the students and teachers, the schoolmate received a stern lecture from the fire chief. The student was suspended from school for two weeks.
A cousin went to a private school run by a religious organization. The teacher punished students by using a thick stick to slap the open palms of the student's hand.
(where were)
(aloud allowed)
(principal’s principals)
In the context of your sentence, the plural noun is what you’re trying to express, as evidenced by the verb “were” that follows it as opposed to the verb “was”, but by using the apostrophe, you have inadvertently changed the plural noun to a singular possessive noun.
ONeg-84 