As tense high school seniors wait for college acceptance letters this spring, their younger siblings also may be waiting to hear from Harvard, Stanford or other prestigious schools — where they've applied for academic summer programs.

More than 250 public and private colleges and universities now offer programs; one admissions officer said her school has been inundated with applications — 400 for 40 spaces. She asked not to be named for fear of generating more.

The scope of programs has grown as well. Students now can try computer-integrated surgery at Johns Hopkins in Baltimore or avert a simulated world crisis at Georgetown in Washington, D.C. Classic subjects — journalism, debate and creative writing — also are popular.

Why the boom? Maybe because these programs provide an opportunity to study topics not available in most high schools; they also pump up students' résumés and let them "test drive" a potential career or expensive college without making a long-term commitment.

Colleges favor summer programs because they generate income from facilities that might otherwise go unused in summer months; plus, they draw student interest to the school. At Boston University, 40% of summer participants apply for college; at Northwestern, it's 50%.

Rachel Vargo, a high school senior in Carmel, Ind., attended Duke's program last summer. She had expected to go into medicine but "wanted to explore different options." She studied political science with Duke freshmen and sophomores as well as pre-college peers. She now hopes to major in it and go on to law school.

Program costs range from about $1,000 to $7,000, depending on the course, the school and the size and duration of the program. Though that might seem expensive for classes that last only four to six weeks (the average cost for one year at a four-year public college is $4,694), many programs offer financial aid. Still, the cost is worth it to many parents, who believe attendance will increase their teen's chances of being accepted into that school in the fall.

But summer programs may not be the foot in the door that many believe. First, schools do not always use their own professors. Though the quality of instruction may be no less, "the potential value in helping with admission" may be limited, says counselor Carl Schulkin of Pembroke Hill, a private school in Kansas City, Mo.

Other counselors discourage kids from attending if they are not certain that the school's own professors will be teaching, simply because the experience might not result in a letter of recommendation from an insider at the school.

Laura Miller, a counselor at North Shore Hebrew Academy in Great Neck, N.Y., suggests that students arrange summer internships instead. She notes these are less common, so they tend to get noticed by admissions officers.

Still, many students feel pressure to attend, even if they're not that interested in the program itself. "Unfortunately, many well-off parents believe they must encourage their children to pursue these summer programs as a prerequisite for admission to what they believe are prestigious colleges," says Rob Killion, director of admissions at Haverford College in Haverford, Pa. But "I've very rarely seen summer courses make any difference."

Admissions officers at Johns Hopkins, Stanford and Harvard say summer programs do not factor in at all; those at Duke, Northwestern and Boston University said they look at them but don't favor a program associated with their school over another.

That doesn't mean teenagers should give up and start looking elsewhere for something to do this summer. Several college counselors said that if a student finds a program specifically for his or her interests, it can strengthen an application by showing passion for and commitment to the subject.

Not to mention the skills students learn. "I'm more independent, and I know how to write papers and study for college classes," Vargo says. "I know I can handle college-level coursework." Now, she hopes, Duke knows it, too.