Every year, thousands of fresh-faced teachers are handed the keys to a new classroom, given a pat on the back and told, "Good luck!"

Over the next five years, though, nearly half of those teachers will transfer to a new school or leave the profession altogether — only to be replaced with similarly fresh-faced teachers.

We've been reporting this month on the pipeline into teaching — and hearing from teachers themselves about why they stay. Richard Ingersoll, who has studied the issue for years, says there's a revolving door of teacher turnover that costs school districts upwards of $2.2 billion a year.

Richard Ingersoll is a University of Pennsylvania professor who studies teacher turnover and retention. He says the constant teacher churn costs school districts more than $2.2 billion annually.

One of the reasons teachers quit, he says, is that they feel they have no say in decisions that ultimately affect their teaching. In fact, this lack of classroom autonomy is now the biggest source of frustration for math teachers nationally.

I spoke with Ingersoll to ask him about his research and what schools can do to fix the problem.

(Read more at NPR)