Advanced Placement enrollment has more than doubled over the past decade as more high schools open up classes to less-prepared students and try to boost participation by lower-income and minority students, writes Jenny Brundin of Colorado Public Radio.

However, taking an AP class doesn’t help students who don’t pass the exam, concludes Philip Sadler, director of the science education at Harvard’s Smithsonian Center for Astrophysics.

Sadler conducted three studies of more than 20,000 students, he said at an Education Writers of America seminar in Boston. Students who earn a 1 or 2, equivalent to an F or D, on the AP science exam don’t earn higher grades in college or perform differently than similar students who never took an AP course.

AP teaches college content — for those who learn it — but doesn’t expose students to the “learning milieu” of college, he said.

In an AP course, he said, the class size is typically small, the teacher keeps tabs on students every day and monitors their progress. That doesn’t happen in college.

Jason Manoharan, a vice president at the College Board, said students who score a 1 or 2 on an AP exam are more likely than non-AP classmates to graduate from college on time. He said 10th grade PSAT scores show hundreds of thousands of students have “AP potential,” which means a better than 60 percent chance of earning a “3” or higher on an AP exam. But they don’t take them.

“Those students are disproportionately minorities, disproportionately low-income,” Manoharan said. “These are kids who would likely pass an AP exam if they took one.”

Sixty percent of students who take an AP exam earn a 3 or higher, Manoharan said. That proportion has remained steady for a decade, even as AP participation has soared.