Most Americans love to reminisce about their first paying job, whether it was scooping ice cream, babysitting, or working behind a retail counter. It was rarely glamorous, but earning that first paycheck was a point of pride and marked a milestone in a teenager's life. By the time Andrew Sum entered his teenage years, he'd already held a job delivering newspapers. Now as an economist, one of his chief concerns is the state of the labor market for today's teenagers. The employment rates for teenagers, ages 16 to 19, plummeted from 45 percent in 2000 to just 26 percent in...