NASHVILLE, Tenn. -

Tennessee teachers are challenging a proposal that would tie professional teaching licenses, to student test results.

Tennessee's largest teachers' union is against using the Tennessee Value-Added Assessment System, which measures how much students improve in a year.

Right now, teachers' licenses are renewed for ten years, without regard to teacher effectiveness.

Under the proposal, renewal would depend on 50 percent of the testing data.

The state board of education is scheduled to vote on the proposal Friday.