Instead of finding them interning in an office or behind a fast food counter, these days, you’ll find many teens in some sort of summer school. Forty-two percent of teenagers were enrolled in classes last summer — almost four times the number of students enrolled in summer school in July 1985. By 2024, teenage workers will make up just 26 percent of the workforce, a reduction of almost half since 1948 when the same age group accounted for more than 52 percent of workers.

Increased competition, older workers returning to the workforce and weak economic growth are all contributing to the decline of teenagers in the workforce. But as schoolwork grows increasingly intense and homework eats up more time, data suggest the biggest reason some teens won’t be working this summer is that they simply don’t have time.

“Students are paying more attention to course work and spending more time on school activities,” said Teresa Morisi, branch chief of the Division of Occupational Employment Projections at the BLS.

Coursework isn’t getting any easier either. Between 1982 and 2009, the percentage of high school students taking advanced math classes, such as Calculus, Geometry and Algebra II, has more than doubled. More students are taking Statistics and loading up on foreign languages.

“Nowadays kids are consumed with their homework,” said Marni Halasa, an ice skating instructor in New York City who coaches about 10 teenage girls, including Monaco. None of her students are working this summer. “There is a constant emphasis on reaching these outrageously high standards. It takes a tremendous amount of time.”

For college-bound teens, some teachers even advise students not to waste their time with a summer job.

“Some of my students only have about six weeks off in the summer,” said Shannon Reed, a lecturer at the University of Pittsburgh and a former high school English teacher. “I could never advocate that they get jobs during that short break. They should rest.”

But the stress could be getting to them. “I see a very high rate of self-reported mental illnesses in my students’ writing,” Reed said.

Maggie Williams, 17, a high school junior in Kensington, Maryland, said she’s under constant pressure to maximize her time.

“I cried today because I was scared for my future,” said Williams, who took four Advanced Placement classes her junior year and will take four more next fall. She’s also involved in several student clubs.

Teens who do want to work are faced with increased competition from a flood of available workers. In Bellingham, Washington, Kaylie Hudson, 17, spent five months looking for a summer job before she found a job at at Target store.

“Employers are offering more jobs to college students because they have more experience and are available full-time,” she said. “Even fast food companies are hiring people upwards of 50.”

In 2016, the median age of retail employees was 37.9 years old, according to government figures. In the leisure and hospitality industries, which have historically been dominated by teenagers, the median age is now 31.3. And in restaurants and other food service trades, where most teens look for work, the median age is 28.6 years old.

Teenagers, with fewer skills and less time on their hands because of school work, are often hit the hardest when there is a shortage of work. And as the minimum wage continues to shoot up throughout the nation, many employers are more likely to hire someone older.

“It’s Friday night and employers don’t have to worry about the older person blowing off work for a party,” said Paul Harrington, a professor at Drexel University in Philadelphia, who has studied teenagers in the labor market.

Young people who don’t work may be missing out on valuable skills that they’ll need later in life. Early work experiences teach reliability, financial intelligence, self-control and help people learn to navigate adult situations.

“Early work experience is a human capital building activity that develops social and behavioral skills that are essential to job market success,” Harrington said. “When kids are working they develop labor market savvy.”

But back in the Big Apple, Monaco, who plans to attend Harvard in the fall, isn’t fazed by her lack of work experience.

“Maybe I missed out on a couple of life skills by not working, like the harsh reality of work,” she said. “But I don’t think it will harm me in any way.”

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This article originally appeared on USA Today.