This week, schools in Baltimore City and across Maryland are administering the state standardized tests in reading and math for students in the third through eighth grades. There's a lot riding on the outcome.

Among other things, the test results will help determine how much students are learning, whether the schools they attend are improving or falling behind, and perhaps even whether some individual teachers and principals keep their jobs.

The test will also play a significant role in decisions about which schools are allowed to remain open and what their level of funding will be.

With so much at stake, it's vital to ensure the reliability of the test results. No one will believe schools are making progress or that teachers have been effective in the classroom if there's a suspicion that the test scores have been tampered with.

That's why city schools CEO Andrés Alonso was right to bring in hundreds of retired educators and substitutes this year to serve as test monitors. The monitors will be stationed in every middle and elementary school, and their job will be to observe the exams and troubleshoot problems in order to guard against cheating incidents like the ones uncovered in previous years.

Currently, there are investigations at 16 city schools where school officials suspect some form of cheating may have occurred in recent years. The tell-tale signs included thousands of erasure marks on test booklets indicating wrong answers had been changed to correct ones, and precipitous drops in test scores at some schools when extra monitors were brought in to scrutinize the process. Having learned from those problems and acting to prevent their recurrence, this year Mr. Alonso is focusing even more effort on making sure the tests are properly administered.

School principals ought to be gratified to know that their efforts to improve the quality of instruction and boost student achievement can only gain in credibility from the monitors' presence. But instead, some principals and their union appear to resent the extra scrutiny, and that's troubling. Their apparent reluctance to embrace a robust regimen to validate the test results sends a terrible message about the transparency of the process and the system's commitment to honesty and integrity. At worst, it makes them look as if they have something to hide.

Mr. Alonso is taking unprecedented steps to prevent cheating, to the point of spending about $360,000 this year to put the monitors on the school system's payroll as temporary employees. But that's money well spent if it leads to better decision-making about how to sustain the gains that already have been made and points to areas where improvements are still needed.

Mr. Alonso also undoubtedly realizes that his work — and that of thousands of teachers, students and parents as well — is put at risk when the public suspects that gains on standardized tests aren't genuine. Documented cases of cheating in a few schools have already fed a predictable cynicism that the only way test scores could be going up is if someone is cooking the books. It's the same story that occurs in Baltimore whenever the police report declines in crime. For some reason, people find it impossible to believe that Baltimore's problems could actually get better.

Mr. Alonso and everyone else in the city school system need to nip such suspicions in the bud. But that will only be possible if school officials and the public they serve are confident that the test scores are unimpeachable.