A Brooklyn teacher may be getting a lump of coal in their stocking this year for Christmas.

Parents at a Park Slope school were upset after their children came home crying Monday because their substitute teacher told them some unsettling news.

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"It's three weeks before Christmas," One mother told News 12. "These kids are 6 years old."

She said she knows each family believes different things: "It's what makes New York City great. There's still this magic of childhood."

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The principal of P.S. 321 said she was "extremely upset" to hear about the substitute teacher telling kids that Santa Claus and the Tooth Fairy aren't real during a lesson about "convincing."

The act landed the teacher on the naughty list, according to the principal.

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"I guarantee you that this substitute will not be in class 1-216 again," She said in a letter to parents. "We take this very seriously."