(Harrisburg) -- The state’s education secretary is backing legislation to change the way school teachers are graded. There are two kinds of teachers in Pennsylvania: the satisfactory and the unsatisfactory. At least, that’s as detailed as the current evaluation system gets. Add some nuance, says the state Education Secretary Ron Tomalis, and base the score on student performance. That way, he says, teachers might start getting real feedback and serving students better. "Our current law doesn’t allow to factor in student achievement into the evaluation system," he says. "The main mission of our system, the highest priority of all -- students achieving academically -- is not allowed to be part of our evaluation system." The proposed rubric for grading teachers has four possible scores, from "distinguished" to "failing." Teachers unions say they support an overhaul of the evaluations system, but caution against using an ill-defined measure of student achievement or implementing the new ratings too quickly.