A new study establishes a link between Michigan's teacher turnover and when teachers were hired. It finds, not all that surprisingly, that teachers hired after the school year has begun are much less likely to stick around than those hired before the start of the school.

And, of course, late hires—who tend to be older, more experienced and more likely to be working on part-time status—are more likely to land in lower-performing urban schools, where filling vacancies is a lot harder.

But their relatively high turnover rates appear to have more to do with the teachers themselves than the schools they end up in. Even when controlling for school "desirability," the late hires were still more likely to leave.