The teacher, Damiana Ebeid Abdel Nour, 23, of Luxor, Egypt, was fined 100,000 Egyptian pounds ($14,300) for the lesson. Parents of three students complained Nour attempted to promote Christianity during school lessons.
Crowds around the courthouse supported a tougher sentence than the court imposed with Islamist groups calling for prison time, al-Masry al-Youm said Tuesday.
Human rights groups sought the opposite, for Nour to be freed without penalty.
"It is outrageous that a teacher finds herself behind bars for teaching a class. If she made some professional mistake, or deviated from the school curriculum, an internal review should have sufficed," said Hassiba Hadj Sahraoui, Middle East and North Africa Deputy program director at Amnesty International.