The past five years have been hard on teenagers. The decade before that wasn’t much better.

The Wall Street Journal today reported that teenager’s work rates plummeted during the recession and have seen little recovery since. More than 40% of teens worked in the summer of 2007. This year, less than a third did.

But while the recession explains the recent drop, there are also longer-term forces at work. From the mid-1960s to the late 1980s, somewhere between 55% and 60% of teens aged 16 to 19 years old worked in any given summer. The rate edged down slightly in the 1990s, then began to fall precipitously in the 2000s.

The decline in youth employment is part of a broader shift in working patterns. Americans are entering the workforce later and staying in it longer than at any time in history. Andrew Sum, a Northeastern University economist and expert in youth employment, points to a remarkable statistic: A decade ago, a 16- or 17-year-old boy was twice as likely to have a job as his 70-year-old grandfather. Today, the grandfather is actually more likely to have a job than the boy. That’s an amazing shift in so short a period of time.