During the school day at Cedar Hill School in Montville, New Jersey, the unidentified teacher told the first-grade class that Santa isn’t real.
The school principal, Michael Raj, sent a letter of apology home to parents saying he's spoken to the teacher about her "poor judgement in making this proclamation," NJ.com reported.
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He alerted the parents and guardians of what happened so families can “take appropriate steps to maintain the childhood innocence of the holiday season.”
The district superintendent also isn’t happy with what happened in the classroom.
Rene Rovtar said she was “troubled and disheartened by this incident.”
"The childhood wonder associated with all holidays and traditions is something I personally hold near and dear in my own heart," Rovtar told NJ.com in a statement.
There's no word on if the substitute is allowed to work in the district again, The Associated Press reported.