(CNN) -- At a time when test scores are used to determine everything from district funding to whether schools can stay open, they're taking on even broader meaning in Ohio.

Gov. John Kasich has signed legislation that will partially link scores to what teachers are paid.

In Ohio -- and many other states throughout the country -- teachers have traditionally been evaluated by observers who've determined whether the instructors are satisfactory or unsatisfactory.

Evaluations will continue to play a role in Ohio. But by the 2013-14 school year, Ohio public school districts will be giving each teacher a grade, and half of that grade will be based on how much students learn, gauged by their test scores.

Decisions about salary, which teachers to promote, and which ones to fire will be based on these results. Teachers' seniority will take a back seat in the new policy, and all but the top teachers in the state will be evaluated every year.

There are several reasons for the changes. One lies in the state budget, which specifies that student academic growth must determine at least 50 percent of a teacher's evaluation.

Another is the federal government's Race to the Top program. In order to receive funds from it, Ohio is one of several states that have promised to find ways to measure and prove students' academic growth.

A third reason is that Ohio is one of a majority of states that have gotten an Obama administration waiver from parts of the federal No Child Left Behind law. In order to do that, the state has had to devise more detailed evaluations for teachers and base personnel decisions on them.

Some observers point out that the new Ohio law could still be changed or watered down before it goes into effect.