In debates over the best way to prepare teachers some argue that easing entry into teaching is necessary to attract strong candidates, while others argue that investing in high quality teacher preparation is most promising. Most agree that we lack a strong research basis for understanding how to prepare teachers. This paper estimates the effects of features of teachers' preparation on teachers' value-added to student test score performance in Math and English Language Arts. Results indicate variation across preparation programs in the average effectiveness of the teachers supplied to New York City schools. Preparation directly linked to practice appears to benefit first year teachers.