Research on student teaching is clear on this point: student teachers are more likely to be effective if they've learned to teach under an effective teacher. However, policymakers and prep programs alike often assert that they have dipped as far as they can into the well of good prospects who meet that mark, a view that helps to explain why so few places require mentor teachers to be effective.

In an arrangement with Tennessee Tech University's student teaching program, Matthew Ronfeldt (University of Michigan) and a team of researchers conducted a clever experiment to see if the well is as dry as many assert. They provided student teaching supervisors with an ordered list of the best available teachers in the region, based on their instructional performance (measured by value-added and observation ratings), years of experience, and placement information (i.e., grades and subjects taught).

In comparison to their control group (where mentor teachers were identified in the typical fashion, such as asking for teachers to volunteer), those district leaders drawing from Ronfeldt's recommendations were able to recruit substantially more effective cooperating teachers. Not only were these mentor teachers more effective (as measured by observation ratings, value-added measures, and years of experience) than mentor teachers in the control group, but their student teachers also reported feeling better prepared to teach.

This simple intervention identified effective and experienced professionals, previously overlooked, who were willing to serve as cooperating teachers without needing any additional incentives. Ronfeldt and his team suggest that further research needs to take place to determine why this set of experienced and effective teachers had been overlooked by previous recruiting methods.