One thing standardized tests can tell us is whether the grades that teachers give their students actually indicate how much the students know.

When a teacher gives a grade to a student, that grade is based not only on achievement and effort but also on what the teacher expects students in that class to know. But here a problem arises. The teacher may have rather low (or sometimes rather high) expectations for students. The teacher may not want to grade more strictly (or more leniently) than other teachers. Grading scales may have drifted in the school so that most grades are As and Bs, without improvements in achievement. Or, more rarely, grading scales may have drifted in the opposite direction; a C at one school may actually indicate higher achievement than a B at another school.

How hard the student has worked and where he or she is on the class curve are considerations that often figure into a teacher’s grading. But they don’t tell us how well the student has mastered the subject matter.

We know, for example, that in Massachusetts and Texas, teachers have been giving students much higher grades in math than those same students receive on state math tests of the same material. Thus, students in Texas who have failed state tests in algebra have been given passing grades by their teachers, especially in schools with large numbers of poor and minority students. Such grades cheat students. This is the soft bigotry of low expectations.

Judy Codding, the former principal of Pasadena High School in California, tells in the opening chapter of her book Standards for Our Schools (coauthored by Marc Tucker) about trying to determine why her school’s students were not succeeding in math. Wanting to know how much students coming into her school as freshmen knew and what classes they should be placed in she gave them objective diagnostic tests. The “horrendous results” showed that incoming freshmen were much less prepared in math than their middle-school teachers had said that they were.

Perhaps the most amazing aspect is how the opponents of standardized tests respond. They say that the tests are wrong and that the classroom grades are right. Peter Sacks, for example, claims in his book Standardized Minds that the Texas state tests are invalid and that “teachers in the trenches” are accurately grading the students.

A divergence between grades from classroom teachers and scores on standardized tests can be a wake-up call for parents, taxpayers, and school boards—telling us that students don’t really know the subject matter and that teachers are too soft in their grading practices. Getting rid of standardized tests is like getting rid of thermometers, X-ray machines, and blood-pressure gauges in a doctor’s office.