ASHEVILLE - One summer job isn't enough for 18-year-old Jenny Mullen.

Since September, the Reynolds High senior has been whipping up fruit smoothies at Planet Smoothie in the Asheville Mall. Soon, she'll start working as a lifeguard at Rec Park Pool in east Asheville, too.

The reason for taking on two part-time jobs is simple: she needs extra money for college. She's headed to UNC Chapel Hill in the fall to study communications, and any extra money will help.

But working part-time has given Mullen more than a little extra cash in her savings account. Learning how to juggle work, family, friends and other responsibilities has given her a sense of confidence that will help her throughout life.

"It's made me more social," Mullen said. "I've learned how to interact with people."

She isn't alone. Millions of teenagers get a job every summer. Between April and July 2004, the number of employed 16- to 24-year-olds jumped by 2.3 million to 21.4 million, according to the U.S. Department of Labor. That was slightly larger than the 2.1 million increase the year before.

Planet Smoothie owner Erika Clamser said she prefers to hire high school students. All six of her employees are teenagers.

"When it's their first job, they're eager to do a good job and make a good impression," she said. "They're much easier to train."

And making a good impression is key to landing a summer job, Clamser said. She's more likely to hire someone who speaks to her personally when they apply, than someone who just drops off a job application.

Job applicants should also know something about the company, or at least show an interest in the company, before going to an interview, she said.

Students have applied at Planet Smoothie who had never tried a smoothie, Clamser said. They don't usually get hired.

Getting a job wasn't hard for Mullen.

The difficult part for her has been finding time to do homework before the school year ends.

She's taking two Advanced Placement courses hoping to earn college credit in high school. Preparing for her upcoming AP exams hasn't been easy.

Mullen said while her mother supports her efforts to make money for college, she makes sure she doesn't work too much.

"Sometimes I sacrifice my homework for sleep," Mullen said.

A lot of high school students try to work more hours than they should to make money, Clamser said. When students start showing up at work tired, she cuts back on their hours, whether they like it or not.

"I find myself taking on a parental role," Clamser said. "Some kids want to work 30 hours a week even when they're in school, and I think that's ridiculous. School is a full-time job."