The speech of teachers in the classroom represents the school's educational product. Most courts apply to teachers' speech the more deferential standard that asks whether there is a legitimate educational reason for the school board's policy.
One federal appeals court determined that any form of censorship must be reasonably related to a legitimate educational reason. However, many courts are highly deferential to employer interests, especially public school officials. For example, in Fowler v. Bd. of Education of Lincoln County, Ky., a teacher found no protection from the Cincinnati appeals court after she showed an R-rated movie (Pink Floyd -- The Wall) to her class.
As a result, teachers should understand that the traditional First Amendment rights of academic freedom generally accorded to university professors are much more limited in public primary and secondary schools.