"It was something you might do in your junior or senior year [of college], or after graduation," she says. "In the last couple years, though, especially in the Bay Area, that concept of internship has moved to younger and younger people. Sometimes we're seeing even high schoolers have an opportunity to do a meaningful internship.

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This fits with what other internship specialists are seeing: a survey by Millennial Branding and Interships.com found that a significant number of companies support the idea of high school students being hired as interns.

"High school internships are a win-win for both employers and students," says Robin Richards, chair and CEO of Internships.com. "For students, work experience is the key to ensure they make a good career decision and build their professional network. By employing students, companies get exposure to talent early in their career journey."

More focus on skills

A second major trend is that many employers are looking for interns with specific skills, rather than a candidate with a good general skills and the potential to learn about the job and the company.

"More and more, employers want to hire someone who's a little more defined in their skills," Reshwan says. "I see companies looking for something specific, not just, 'Give me a good egg.'" There are fewer employers who are open to just a bright new person. It's more, "Can they have a little experience?"

Reshwan says there are problems with that approach, including the risk of burnout for young workers. However, she adds, the trend may soon peak. "I think it will soften somewhat because as we reach full employment, the ability to get the personality you want and the skills you want will be harder to find," she says. "More employers will move away from requiring something specific as the market continues to heat up."

Basic do's and don'ts

Companies that place interns say there are some basic rules employers should pay close attention to. And many of the rules are not that different than those for regular employees: emphasize good communication, have clear expectations, and be able to measure performance.

Suzanne Lucas, an HR columnist for INC., says companies should be prepared to talk interns through the basics of workplace behavior, since for many, it's their first time in a business environment.

"Things like a dress code may seem screamingly obvious to you, but they aren't to everyone. If you don't have a formal dress code written, write one before your interns start and give it to them," she writes. "Explain that they aren't to use their phones during meetings, that talking about their weekends should involve only things they wouldn't mind their mothers overhearing, and that you can't skip out on a meeting like you would on a lecture."

Lucas and Reshwan agree that interns will do better if given specific feedback on measurable goals.

"Interns aren't looking for you to just say everything's great," Reshwan says. "They're used to an instructor circling a problem or marking the answers they got wrong. So they're open to feedback. Be clear, and if you see problems, coach around them. They're used to be being corrected, so if employers use those methods, it ends up being a great experience."

There is also a good deal of debate around what kind of responsibilities interns should be given. Several placement companies, such as Internships.com, caution that interns should not simply be given menial tasks or treated as gophers. Other sources, such as Lucas, note that there are rules about giving too much responsibility to unpaid interns. The more important the duties, the more likely the intern will need to be compensated. In general, experts say, there should be a mix of duties that emphasize giving the intern an educational experience in the workplace.

Year-round internships

Although most internships take place in the summer, Reshwan says the practice can be used year-round. "A lot of employers don't think about having interns during the school year," she says. "But we've seen plenty of successful internships during the school year, depending on type of work and work schedule. Granted, they won't be available 40 hours a week. But they may be able to come into the office a couple days a week or work remotely."

Recruiting can be done anytime, Reshwan notes.

"There's no harm in starting early—winter break is a great time to talk to potential interns," she says. "You don't have to wait to the spring. Just make sure you keep in touch, because they are younger—and sometimes it's out of sight, out of mind."

In general, employers large and small can benefit from interns. It's a great way to identify potential new talent, increase brand awareness, and lighten the workload on other employees during busy summer months. Reshwan says especially in areas where the economy is doing well, internships can be very helpful in building a workforce. "It's a necessity in a hot market to build that pipeline," she says. "At the end of the day, students want meaningful work, mentorship, the experience of feeling valued. Internships are a way that companies of any size can compete for new talent."