Some judges are relatively lenient. Some are strict. So one offender goes home with an ankle monitor and a curfew while a similar offender gets locked up with a bunch of other troublemakers, removed from family, church, routine and school.
Another conclusion: If you get locked up, your odds of dropping out of school increase.
"You're supposed to be going to school while you're there," Doyle says of the juvenile facility, "but kids aren't there very long, so it's not like teachers are investing in new education plans for them."
In Doyle's study, all the offenders were unlikely to finish high school, but the incarcerated ones were at even higher risk.
Of the incarcerated teenagers, only 2 percent went back to school when they were let out.
That's a lot of 15- and 16-year-olds roaming around with nothing to do and nowhere to go and no adult to watch them.
And the most significant conclusion from the research: By locking up so many juveniles — removing them from their communities, increasing the odds that they drop out of school — we may be seeding more crime.
I asked Doyle if he thought incarceration was helpful for any young people.
"I'm just not sure," he said. "There are the ones all the judges would agree need to be incarcerated, and it's possible those kids are scared straight and go on to better lives."
On the other hand, he said, plenty of research suggests that at 14 or 15, teenagers aren't deterred by stricter penalties.
In the past decade, some states, Illinois among them, have reversed the juvenile incarceration trend that exploded in the 1980s and '90s.
Doyle's research may give the trend even more momentum. He likes that.
But he is not a social worker. He's an economist.
Leave it to others to make eloquent arguments about the injustice of locking up so many young people, who happen to be disproportionately young people with dark skin.
Doyle's research helps make the dry-eyed case that juvenile incarceration, pure and simple, costs too much. The cost of prisons. The loss of individuals' earning power and learning power.
We all pay, and it's a debt that swells far into the future.