Selba Munguia of Miami, Fla., is so determined to be a college student that, like hundreds of thousands of other young people, she has practically become one in high school.

She took three college-level Advanced Placement courses as a sophomore and five more as a junior. Having aced them, she will begin 12th grade at Miami Senior High School with another five AP courses: English, Spanish language, statistics, U.S. government, and world history.

“A lot of people are pushing themselves to take as many AP classes and tests as they can,” said Ms. Munguia, a 17-year-old with eyes on an Ivy League education. “I think it’s amazing that people really care, that they want to be pushed. …They’re looking to their future.”

The Advanced Placement Program, which began as a tiny experiment for top seniors seeking college courses and credit, has swelled to the point of altering the high school experience.

Over nearly 50 years, the number of students taking annual AP exams has grown from about 1,000 to more than 1.1 million, with a 140% increase during the last decade alone.

A few hundred public high schools used to offer AP courses; now two-thirds of them do. By last year, one out of every three public high school graduates had taken at least one AP test. The subject list has more than tripled, from popular core courses such as history and biology to additions in the arts and social sciences, with more world languages coming soon.

Such growth is widely viewed as an education success story, because more students have been given access to training that colleges demand of them.

But some educators see an academic arms race, with students piling up AP courses to impress colleges and schools adding classes without ensuring teachers are prepared for them.

The AP goal remains to challenge students to analyze subjects at the kind of depth found in a college classroom, with a payoff that goes beyond learning. Most American colleges give students who pass AP tests credit or higher placement so they don’t repeat ground.

Yet as more sophomores and juniors take AP courses and exams, their motivation has become not just to prepare for college, but to gain an edge getting into one.

College admission officers place more importance on grades in college-prep courses such as AP classes than they do on any other factor – including SAT scores, grade point average, class rank, and student essays, a 2003 survey found. Colleges give less emphasis to AP exam grades in admitting students, in part because such scores may come in too late in the process.

The AP is not intended as an admissions tool, but the connection makes sense, said Trevor Packer, executive director of the AP Program at the not-for-profit College Board.

Research shows students who have taken two or more AP exams have better rates of completing bachelor’s degrees. And the College Board itself promotes the admissions angle, telling students AP scores can dramatically improve their chances of getting in where they want.

In Ms. Munguia’s school in Miami, where most students are Hispanic and many come from poor families, enrollment in AP courses has tripled over the last five years. The school has expanded tutoring and given awards to AP students to keep them encouraged.

“The old philosophy was that only the very best students were sent to AP courses. We’ve changed that,” said Erick Hueck, who oversees the AP program and teaches AP chemistry at Miami Senior High. “We’re going to be more inclusive. We’re going for the greater good.”

Nationwide, minority participation is improving but remains a challenge. Hispanics and blacks make up 31% of high school students but only 17% of AP test-takers.

Researchers have found that schools have steered minority students away from AP courses, and those who make it in sometimes endure the scrutiny of being the only minority in class.

At Edinburg North High School in southern Texas, where many students are just learning English, all of them are invited to take AP classes. Eva Torres, the dean of instruction, tells teachers not to worry how students do on AP exams as long as they’re engaged in class.

“These students often don’t get the credit they’re due,” she said. “A lot of times people don’t understand that it’s a language barrier they have, not a lack of a capacity to learn.”

Yet Education Trust, a nonprofit that advocates for poor and minority children, says test scores raise questions about whether all AP classes are high quality. In 2003, for example, 69% of white students passed one AP calculus course. Only 34% of blacks did.

Jeannie Oakes, a UCLA education professor, says giving students access to more AP courses without sufficiently preparing them and their teachers is a “cruel hoax.” She served on a National Research Council panel that found AP courses were improperly used to rank schools and that classes lacked the kind of quality standards that the brand name implies.

Each AP class has an outline, not a specific lesson plan. Schools decide whether a teacher is ready for the advanced material. The real check on quality is the AP test, Mr. Packer said. College faculty help shape the exams, craft course outlines, and review them annually.

The College Board is responding to challenges of access and teacher training, with targeted help in rural areas and subsidized courses for middle and high school teachers.

Taxpayers are chipping in, too. Many states now pay for AP course development and test fees, and, in this election year, President Bush wants to double federal spending on the AP to $51.5 million, to expand course access for poor children and training for their teachers.