In 1990, 32 percent of high school students held jobs, versus just 16 percent now. Blame their elders.

Sectors that traditionally have offered teens their first paying gig — fast-food chains, movie theaters, malls and big-box retailers — have now become the last resorts for out-of-work college graduates or older Americans forced back into the labor force out of sheer financial necessity. The resulting squeeze has left students on the outside looking in.

“By definition, teenage workers get the jobs that are left over,” said Charles Hirschman, a sociology professor at the University of Washington who has studied and written about student employment. “When you can’t find someone else to bag your groceries or work construction, often teenagers are the labor force you can count on to pick up that slack for a low wage. But now, with the recession, everybody has moved down. Those jobs aren’t going to teenagers.”