In sports, playing with stronger players improves an athlete's game. And in education, teachers perform better when the quality of their peers improves. That's the gist of new research by two economists who analyzed North Carolina elementary school teachers and students to see what happens to student achievement when the quality of a teacher's peers improves.

This is good research that should introduce a new note into the tiresome How-Do-We-Improve-Professional-Development debates, stuck as they have been on the same refrain for as long as we've been listening (One-shot workshops? Bad! Bad! Bad!).

The authors found that newer teachers are the most sensitive to changes in peer quality. The more colleagues in the school building with more than one year of experience, the more likely it is that a new teacher can produce greater student gains.

Perhaps most interesting is that both a teacher's current and past peers impact her effectiveness. About one fifth of a teacher's own effectiveness is learned as a result of exposure to previous peers. The authors see this finding as an argument against individual performance pay schemes and suggest school-based performance pay may be a more effective model.

Less clear about all these findings is why. Are the gains a result of teachers mentoring one another, or is it the motivation that results from being surrounded by higher caliber teachers?

Either way, there's an important lesson here about effective professional development practices. Placing new teachers--or struggling teachers for that matter--in assignments where they are surrounded by effective teachers seems like the least expensive but perhaps most effective professional development out there.