It happened at MS 391 on Folin Street just before noon.
Preliminarily, it appears the bullet went through the window of a sixth-floor classroom and grazed the teacher in the right palm of his hand.
He was taken to St. Barnabas Hospital where he was treated and released.
During a town hall with Eyewitness News, New York City Schools Chancellor David Banks said the teacher didn't even know he was hit.
"Ne thought a socket popped or something," Banks said. "He's home, thank god. It could have been a lot worse, but he is going to be just fine."
No students were in the classroom as school does not start until Thursday.
Police went floor by floor through the apartment complex across the street, where the shot was likely fired from.
"Let me be clear, this bullet was not fired from inside the school and at this point of the investigation, we believe it was fired from a long distance away, the school was not targeted," said NYPD Deputy Chief Keiyon Ramsey.
One school safety agent was on duty at the time.
"This egregious display of violence is both upsetting and reprehensible," a spokesperson for the Department of Education said. "NYPD immediately responded to the scene where one educator sustained non-life-threatening injuries. We will provide support additional support to this school community."
Out of an abundance of caution, NYPD officials said there will be additional school safety agents and police officers on site to make sure students and parents feel safe.
So far no arrests have been made.
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