18 states have changed their teacher tenure laws this year

Lawmakers in 18 states have passed bills changing the tenure laws for teachers in public schools this year, according to a new report from the Education Commission of the States.

Idaho politicians eliminated tenure for the state's teachers altogether this year, arguing that it makes it too difficult to fire ineffective teachers. (Education Week points out that Idaho voters will have the chance to repeal that law in 2012.)

In most states, tenure is usually granted after three years, and it means administrators must point to specific reasons for dismissal at a hearing if they want to fire a tenured teacher.

Several states, including Illinois and Tennessee, passed laws last year that make it more difficult for teachers to gain tenure, saying that they must show their students do well on standardized tests before they receive extra job security.