Pennsylvania lawmakers should take care in considering a bill that would let school districts use students' test scores to measure teacher performance.

The legislation would mandate a statewide change as early as next year. Standardized-test scores would weigh heavily in determining whether teachers keep their jobs, receive tenure, or get merit pay.

Given the sorry state of education, with students dropping out and flunking at alarming rates, it makes sense to use sterner measures to evaluate teachers, reward the best educators, and show the door to those who continually fail to improve.

It also makes sense to include test scores as a component of teacher evaluations. After all, the federal No Child Left Behind law makes test scores the basis for its rating of schools, so how well teachers do in preparing students for tests is important.

But recent cheating scandals that have rocked public education around the country show the dangers of placing too much emphasis on standardized testing.

In Atlanta, investigators are probing a widespread test-score scandal allegedly involving more than 200 teachers and principals. Similar cheating incidents have been reported in Washington, Baltimore, New York, Los Angeles, Miami, and Orlando.

There have also been allegations about possible test security breaches at two Philadelphia schools that had unexplained increases in test scores. And it was not long ago that Camden Superintendent Annette Knox was forced to resign after giving herself performance bonuses based on rigged test scores.

In many of these cases, educators faced unrealistic expectations and pressure to meet testing benchmarks. But that's no excuse for making decisions that cheated schoolchildren out of a real education. They were taught how to pass a test, but little else.

Union leaders have not fully embraced the Pennsylvania proposal. Instead, they have rolled out their own reform plan to revamp how teachers are evaluated. The two proposals form a good starting point for discussions leading to the best model.

Under the state's current system, teacher dismissals based on poor evaluations are rare. For the 2009-10 school year, 99 percent of teachers statewide received satisfactory ratings. Yet, in the same school year, one in four students taking Pennsylvania's standardized tests missed reading benchmarks, while one in three failed math.

The Pennsylvania State Education Association wants teachers to be judged on test scores as well as classroom observations, portfolio reviews, and students' work. That seems reasonable. State Education Secretary Ronald Tomalis wants test scores to count for half a teacher's rating, but that percentage seems too high if he wants to encourage teachers to do more than teach to the test.