The oft-expressed obstacle to youngsters entering the labor market was that you couldn’t get a job without experience and without a job you couldn’t gain any experience.

The answer to this was traditionally the summer job, something low-paid, often demanding not always challenging, but that at the end of the summer resulted in the all-important first reference from an employer: “The kid shows up on time, works hard and doesn’t complain.” No matter how humble, it was a first step on the career ladder.

But summer jobs for teenagers, “once a rite of passage to adulthood,” as the Associated Press put it, are disappearing.

According to government figures and AP interviews, in 1978 the percentage of employed teens peaked at close to 60 percent and remained generally above 50 percent until 2001.

Since then, propelled by two recessions plus competition from unemployed adults, immigrants and debt-saddled college grads, the employment rate for teens ages 16 to 19 fell to 29.6 percent last summer, the lowest since World War II. The outlook for this summer doesn’t seem any brighter.

And it’s not for lack of demand: more than 44 percent of teenagers who want summer jobs can’t find them or can’t find jobs that give them enough hours.

There is an abundance of anecdotal explanations, some of them contradictory. Some teens are opting for summer schools, music and language camps and volunteer programs to build resumes for college admissions.

But these are teenagers from relatively well-off families and they are also the most likely to find summer employment. Last summer, 44 percent of white teenagers who come from families with income between $100,000 and $150,000 found work.

Those who need the work the most, both for the money and the experience, fare the worst: Only 14 percent of black teens from families making less than $40,000 found work last summer.

The worst possible outcome, according to a Federal Reserve study cited by the AP, is that that the teenagers do nothing except hang out, sleep, watch TV and play video games.

Adult competition is only part of the story: Technology has eliminated many unskilled jobs; strained state and local government finances have killed or curtailed summer jobs programs; regulations have limited the kinds of jobs teenagers can hold and the hours they can work them; and insurers’ liability concerns have made some employers hesitant to hire youngsters.

Another, bigger part of the problem is the continued increases in the minimum wage, which have made it more expensive for employers to fill the kinds of jobs that so often go to inexperienced — but willing — teens.

Labor analysts note that there are jobs going begging that don’t require college degrees but do demand certain specific skills. Having unemployed teenagers wasting their summers is not going to fill that gap.