Mentoring has become an extremely popular policy for improving the retention and performance of new teachers, but we know little about its effects on teacher and student outcomes. I study the impact of mentoring in New York City, which adopted a nationally recognized mentoring program in 2004. I...

We use six years of data on student test performance to evaluate the effectiveness of certified, uncertified, and alternatively certified teachers in the New York City public schools. On average, the certification status of a teacher has at most small impacts on student test performance....