Congress has so far been reluctant to revise its No Child Left Behind law, despite its flaws. The problem may be that the issue has gotten too much attention: Whether legislators loosen or tighten federal controls over public schools, they are going to offend someone.

It is easier to interfere with instruction when no one is looking, as happened in December when Congress sharply reduced funds to pay Advanced Placement and International Baccalaureate test fees for low-income students. The legislators chopped the allotment from $43 million to $27 million, a gross lapse in legislative insight.

We have plenty of data showing that taking an $87, three-hour AP test is one of the most cost-effective ways to prepare for college. Studies of hundreds of thousands of students by Linda Hargrove, Donn Godin and Barbara Dodd in Texas and Paul Geiser and Veronica Santelices in California show that students with passing scores on AP do better in college than students who don’t take the test.

Those difficult exams, full of essay questions, not only give high- schoolers a taste of college trauma but also motivate harder work in the course by them and their teachers. The exams are written and graded by outside experts and cannot be watered down to save the reputation of students who didn’t do their homework or instructors not up to the job.

AP and IB were designed for students from affluent families and demanding high schools. But in the past 30 years, teachers have discovered the power of the courses and exams to change the lives of poor children. Last year, according to the College Board, 375,439 low-income students took 615,315 AP exams — 23 percent of the total taken.

Because of the cuts, low-income students will have to pay $15 each for their first three exams and $53 for each additional one. The College Board estimates 29,000 low-income students nationwide will be deterred by the costs and take fewer exams than they would have otherwise.

Since two teachers at Garfield High School in East Los Angeles in 1987 produced 26 percent of all the Mexican American students in the country who passed AP calculus exams, the potential for low-income students to succeed when given enough time and encouragement to learn has been obvious. But Congress cut the subsidies anyway because the victims were too young and powerless to complain.

The effects of the cuts are now being observed in California, where Los Angeles Times reporter Stephen Ceasar recently cited several instances of students suffering from the funding changes.

In the Washington area, with more resources and much larger AP and IB programs, the losses so far appear less serious. Fairfax County schools spokesman John Torre said no AP or IB students, rich or poor, will be charged test fees this year. Bill Heiser, principal of North County High School in Anne Arundel County, said the fee for low-income students will be subsidized.

And Frazier O’Leary, a veteran AP English teacher at Cardozo High School in the District, said the D.C. schools have long protected his students from having to pay for AP. “They don’t even know how much the tests cost,” he said.

The College Board also increased its subsidy for low-income students from $22 to $26 per test. Asked why the nonprofit group doesn’t cover the entire fee, Trevor Packer, College Board vice president for AP, said that for most of its history, AP costs have exceeded revenue: Money is needed to pay the professors and high school teachers who grade the exams and to train more AP teachers.

Some IB schools charge test fees. Some don’t. But the small U.S. headquarters for IB does not subsidize any low-income students.

AP and IB will continue to grow since so many teachers believe in them. In time, Congress will get that, but for now, many disadvantaged students are being told they can’t take a test that will help them do well in college unless they can find the money.

To read previous columns by Jay Mathews, go to