Unlike tenure for university professors, tenure for K-12 teachers does not, in theory, shield them from dismissal. Instead, it's simply a guarantee of due process — that if a teacher is fired, it will be for cause.
The advent of tenure, which coincided roughly with World War I and the suffragist movement, was meant to protect teachers, who, in olden days, were often fired for reasons that had nothing to do with their work, including race.
Teachers were often let go when a new political party came to power locally, or if the principal wanted to hand out jobs to his friends, or even if a teacher got pregnant.
"These laws were passed in state after state to protect good teachers from arbitrary actions," says Dennis Van Roekel, president of the National Education Association, which is the country's largest teachers union.
"Due process is necessary in order to avoid the type of abuses of the past," he says. "It's very upsetting that in 2010, under the guise of improving schools, we suddenly get rid of protections from firing teachers for inadequate or wrong reasons."
via npr.org