Looking at the chart above, Matthew Yglesias concludes that kids who drop out of high school are making a terrible decision:

This kind of thing makes me wonder how much of a difference could be made by pure information. How many 14 and 15 year-olds are aware of this correlation? How might their behavior—and that of their parents—change if they were better informed? My dad dropped out of high school and he’s turned out fine, but I think that still wasn’t a decision with a positive expected value. People suffer from optimism bias that can be further exacerbated by bad information. After all, it’s not totally obvious what job-relevant skills one learns in 12th grade.

His premise is that deciding to stick it out through high school would move an individual from the blue line to the red line. Without seeing the data, I strongly suspect otherwise. I'm guessing the things that make people unable or unwilling to finish high school also make them bad at acquiring and holding jobs. Which is to say, even if you took the high school dropouts and managed to get all of them through school, giving them the benefit of additional school knowledge but not changing anything about their work habits, health, intelligence, environmental pressures, and so on, they'd have much higher levels of unemployment anyway.

I don't think you learn a lot of job-relevant skills in 12th grade, and I suspect even the signalling value to employers of a high school degree is not all that valuable, either.