For fun this summer, Mario Zubia spent six hours a day, five days a week in a Caltech classroom studying neuroscience and physics. He topped it off with five hours of homework a night. And the 17-year-old Santa Maria resident did it by choice.
"Some of my friends are like, 'What's wrong with you?' " said Mario, chuckling. "A high school counselor told me about it. I always liked science and math, and it seemed like a great opportunity."
Teens such as Mario -- who eschew such summer rituals as hitting the beach in favor of hitting the books -- appear to be growing in number, according to high school and college administrators.
Students' specific goals vary: improving SAT scores, gilding college applications or just freeing up class schedules so they can fit in yet another Advanced Placement course or internship.
But their motivations are much the same: boosting their chances of getting into top colleges at a time that may be the toughest ever, thanks to a population peak of high school seniors, greater rates of college attendance and a stagnant number of college slots.
"It's more competitive today to get into your college of choice than ever before," said Carl Hampton, principal of Chino Hills High School.
Hampton said he was seeing more and more students taking summer classes and tutoring to burnish their college applications, including his nephew, who just enrolled at the Air Force Academy.
"Unfortunately, it's just something that's become necessary if you want to get ahead," he said. "To get accepted into some schools, the competition is so steep, and they have to decide if that's worth the price."
His nephew has no regrets, but Hampton said he worried that some students may miss out on the time to be carefree teenagers.
"I worry about that," he said. "I think some of the creativity gets kind of drilled out of them."
As a new school year begins, students such as Julia Chang, 16, who attends Oaks Christian School in Westlake Village, say the results will make their summer sacrifices worthwhile. The Calabasas resident spent eight weeks of her summer immersed in an SAT boot camp run by Elite Educational Institute, which was founded more than two decades ago in a Koreatown storefront and now runs 18 centers in California, six in Canada, five in South Korea and one in Thailand.
At the institute's Northridge campus this month, hundreds of teens hustled between classrooms, devoting five hours a day, five days a week to math, reading comprehension and writing classes and taking one full-length practice test each week.
Their goal is to boost their scores on the 2,400-point, three-part college entrance exam, helping their prospects at the nation's most competitive colleges.
"It's a lot of hours, it's intense, we have homework," said Julia, who hopes to study theater or pre-med at Georgetown University. "My parents are kind of making me, but I know it will be totally worthwhile when I take the SAT."
Mario, who attended Caltech's Young Engineering and Science Scholars summer program, said he hoped it would increase his chances of attending the school once he graduates from Santa Maria's Ernest Righetti High School.
The Caltech program, which attracted 67 applications in 2002, received 459 last year. Fewer than three dozen are accepted each year. The students then spend three weeks living on campus, taking classes, doing lab experiments and completing research projects. They also meet with university admissions officials, faculty and current Caltech students.
Students are also using their summers to take classes at local community colleges, so they can complete high school requisites, which will free up their schedules so they can take more electives or high-level classes.
At Saddleback College in Mission Viejo, 940 high school students took classes this summer, an enrollment that has nearly quadrupled since 1999.
"The jump is because high school students are starting earlier to work on their college degree," said Jenny McCue, spokeswoman for the college.
McCue, 36, said that when she was in high school, she spent her summers working and hanging out at the beach with friends.
Today's teens are different, she said.
"They're very ambitious; they seem to have a much clearer vision of what they are going to do with their lives than my peers did when I was in high school. They know where they want to go, they know where they want to be and they know what they're going to do to reach those goals. It's really impressive."
Tania Khodayar, 15, who will start her sophomore year at Mission Viejo High School next week, is among those students. Over the summer, she took an introduction to fine arts class to fulfill her arts elective requirement, which means the Laguna Hills teen will be able to take additional Spanish classes in high school or possibly intern at a doctor's office during her senior year. She also took an SAT prep class at Saddleback.
Tania, who hopes to attend USC or a University of California campus and become a surgeon one day, says she plans to take more courses next summer.
"I'll get another subject at school over with," she said.
Tania said she had been concerned that her busy schedule would cause her to miss out on time with her friends, playing tennis, visiting museums and having sleepovers.
"I was worried I wouldn't have time to enjoy summer -- I worked so hard over the school year," she said. "It wasn't as bad as I thought it would be. My best friend was in the SAT prep class with me."