In 2010, Teach For America (TFA) launched a major expansion effort, funded in part by a five-year Investing in Innovation scale-up grant from the U.S. Department of Education. To examine the effectiveness of TFA elementary school teachers in the second year of the scale-up, we recruited thirty-six schools from ten states and randomly assigned students in participating schools to a class taught by a TFA teacher or a class taught by a comparison teacher. We then gathered data on student achievement and surveyed teachers on their educational background, preparation for teaching, and teaching experience. The TFA teachers in the study schools had substantially less teaching experience than comparison teachers but were more likely to have graduated from a selective college. Overall, TFA and comparison teachers in the study were similarly effective in teaching both reading and math. TFA teachers in early elementary classrooms (grades 2 and below), however, were more effective than comparison teachers: TFA teachers in prekindergarten through grade 2 had a positive, statistically significant effect of 0.12 standard deviations on students' reading achievement, and TFA teachers in grades 1 and 2 had a positive, marginally significant effect of 0.16 standard deviations on student math achievement.