"You can't manage what you can't measure," goes the well-known business adage, which is why most successful companies review their performances regularly throughout the year.

The same should go for the nation's 90,000 public schools. Fortunately, the White House and Congress are considering ways to hold schools accountable by requiring that states annually test all students from third through eighth grade in reading and math.

Nancy Ichinaga, retired principal of the Bennett-Kew Elementary School in Inglewood, Calif., and a recent addition to the California Board of Education, agrees that it's necessary to test. "Every profession uses objective measures to determine effectiveness," she says. "Education should be no different."

Ichinaga should know. She used regular testing to solve a problem too many educators think can't be solved: the abysmal academic performance of low-income children.

When Ichinaga became principal of what was then the Bennett School, average test scores were in the bottom 3 percent of the nation. Within a few years, she turned the school into one of the highest performing in all of Los Angeles County. Even though four out of five of Ichinaga's students qualify for the federal free and reduced-price lunch program, they performed at the 62^nd percentile in reading and the 74^th percentile in math last year.

Why the change? Ichinaga credits the success to a research-based curriculum -- and to testing students' mastery of the content every six to eight weeks.

In communities across the country, you can find public schools where low-income children excel academically. At almost every single one of them, frequent testing enables the principal and teachers to ensure that, yes, "no child is left behind." Testing is a crucial barometer: It lets teachers know which students require extra help. It also lets principals know which teachers are most effective and which need additional training.

"The more you test, the better the students do," says David Levin, the principal of the KIPP Academy charter school in New York City, the highest performing middle school in the Bronx. "There has to be constant assessment in place that demonstrates real mastery of what you are teaching."

Ernest Smith, who runs Portland Elementary in rural Arkansas, credits testing with the remarkable results he has achieved among low-income students. Until it started regular testing, "the school had no idea how poorly it was doing," says Smith. "Now every teacher is aware of the national percentile ranking of every one of her students. The difference shows."

Successful teachers understand that "teaching to the test" is fine, as long as it's a good test. No teacher would think to give students, say, a spelling test without providing them with the list of words. Students know exactly what's going to be on the test and are given an entire week to practice and review. That's "teaching to the test."

These teachers also insist that regular testing doesn't take time away from their jobs. Rather, it helps them use their teaching time well. At Drew Elementary School in Washington, D.C., Principal Steven Roseman ensures that all students are tested every eight weeks as part of the school's "Success For All" program. Teachers fill out forms showing their students' results and give them to Roseman so he can monitor student growth.

These "performance reviews" seem to work: Drew's average test scores in math were in the 74^th percentile last spring, despite the fact that almost every student in the school qualifies for the free or reduced-price lunch.

Regular testing not only improves student learning and teacher quality, it improves student discipline. According to Thaddeus Lott, director of several successful inner-city charter schools in Houston, "disruptive and disobedient children are either bored or frustrated. The easiest way to maintain order in a school is to teach to everyone's appropriate instructional level." How do schools make sure all children are being challenged? Easy, says Lott. Test every child constantly to measure what he or she knows.

Holding students to high academic standards without regular testing is like expecting high returns from a business without being able to check its quarterly earnings reports. We can't expect to know whether our students are learning unless we test them regularly throughout the year. Anything less just doesn't add up.

Megan M. Farnsworth, a former curriculum specialist and teacher at high-poverty schools in Burbank, Calif., is a Bradley fellow at The Heritage Foundation (www.heritage.org).