The incident was the final straw after the 'Firework' hitmaker had previously been given a "clear warning" following "several" other incidents of inappropriate behaviour.
The note continued: "This suspension comes after she several incidents and a clear warning in a previous conference.
"On October 17, she was called into my office to discuss her use of inappropriate language ('p***ed off' and calling 3rd grades 'brats') and using the Lord's name in vain (saying, 'oh my God').
"She has also admitted being previously involved in playing 'Spin the Bottle' and 'Truth or Dare' which resulted in students kissing on the cheek. She was told then that any more inappropriate behaviour would result in a suspension.
"Katy was seen by two teachers recently outside their classrooms doing the Macarena dance in which she made body motions with sexual overtones (described by one teacher as being 'like an exotic dancer'. "
And the 'Chained to the Rhythm' singer had also been reprimanded for inappropriate clothing.
The letter explained: "Katy has been cited twice for wearing 'crop tops' with her midriff showing. Mrs. Hudson has assured me it won't happen again."
When she posted the note onto her Instagram Story, Katy added the caption: "WHEN I WAS SUSPENDED IN 6TH GRADE FOR HUMPING A TREE AND I GUESS OTHER STUFF.(sic)"
-Bang! Showbiz