John Freshwater, a science teacher at Mount Vernon Middle School near Columbus, Ohio, used a device known as a high-frequency generator to burn images of a cross on pupils last December, according to a report for the school board.
While he claimed he was trying to demonstrate the electrostatic tool to students and described the image as an "X" rather than a cross, the report - carried out by independent investigators - insisted it was a cross.
The family of one child filed a federal lawsuit against the teacher, claiming that his civil rights had been violated. They said the cross remained on his arm for three or four weeks.
The report by the school board also accused Mr Freshwater of undermining science education by discrediting evolution and focusing on creationism. It also said he kept a Bible on his desk.
Mr Freshwater is appealing the decision. Some of his students told investigators he was a "great guy" and their favourite teacher.
