In recent years, many advocates for low-income students have worried that the growing popularity of Advanced Placement courses was placing disadvantaged students at a further disadvantage. Since wealthier high schools offer more of the courses, and colleges value them in admissions, the theory goes, AP credits were one more way that inequitable educational opportunities were holding some students back.

A new study of an unusual program in Texas, however, suggests that AP can be a tool in promoting better college preparation and a more rigorous high school education. And the new study suggests that a financial incentive can have a positive impact on student performance.

The study, "A Little Now for a Lot Later," found that adoption of a program that offered cash to students in disadvantaged high schools who pass AP exams and the teachers who instructed them resulted in numerous gains. Not surprisingly, more students took AP courses and the exams and passed them. But the benefits extended well beyond that. Among participants, there was a 30 percent increase in the number of students scoring at least 1100 on the SAT or 24 on the ACT, and there was an 8 percent increase in the number of students who matriculated to a college in Texas.

C. Kirabo Jackson, an assistant professor of labor economics at Cornell University and the author of the study, said it was unclear why the financial incentive was having an impact, "but it is clearly sending a message to the students." The study was published on the Web site of the Cornell Higher Education Research Institute.

Jackson analyzed high schools in Texas that participate in the Advanced Placement Initiative Program, a privately funded effort in which philanthropists contribute to provide financial incentives for the AP program, training for teachers on the courses, and outreach to students on preparing for the courses. The program has been offered only in economically disadvantaged areas, so while some of those high schools may have students who are wealthier than average, the overall pool was of high schools that don't have much in the way of money or AP programs. The payments -- both for students who score at least a 3 on the AP exam and for their teachers -- are $100 to $500 each, with different high schools offering different amounts.

While Jackson said that the money had an impact, he stressed that there was more than cash involved. Students who don't take the right courses early in their high school careers can't just jump into AP work, he noted, and the fact that the largest gains took place when the incentives were in place for three years suggests that students were hearing about the program and making curricular choices early.

Guidance counselors reported to Jackson that the program "changed the culture" of the schools. Teachers had an incentive to "be more inclusive" in recruiting students to AP courses, and students adopted a new attitude about AP. "It used to be uncool," Jackson said.

In a follow-up study, Jackson plans to focus on exactly why the money made a difference and also to look at what happens to these students in terms of academic success in college, where there is not an additional financial incentive. "Does this actually generate interest that is long lasting or does it die down?" is the question he said he would like to answer.

He thinks that there may be "an intermediate cause" for the success -- as much about the attention the incentive creates for academic preparation as about the cash. "I am reluctant to say we have a policy where we throw money at kids, and hope they make the right decisions," he said. But of the Texas effort, he added, "it does seem to work."