How do you measure a good teacher? Surely, the most important yardstick is his or her students. If they do well — if they learn basic reading and math — you can be pretty sure the teacher is doing his or her job well. If they consistently fail to demonstrate proficiency, or at least improvement, then the teacher might do better to seek a new career.

On Friday, The Examiner’s Lisa Gartner reported that District of Columbia Public Schools will be changing its teacher evaluation system — known as Impact — once again. This time, the changes will weaken the influence that basic math and reading test scores will have on teachers’ evaluations. Currently, they account for half of a teacher’s evaluation score, but under the new system they will account for only 35 percent of it.