In this publication, researchers at the RAND Corporation identified the relationship between teachers’ characteristics and improved learning outcomes in Math for English Language Learners (ELL), a group that generally does not perform as well as their peers. Using data from the New York City public school system, the authors examine a number of factors, including teachers’ own test performance, their experience teaching ELLs, and whether or not they had received professional development specific to ELL instruction. Results showed that novice teachers’ effectiveness improved based on prior-year experience teaching ELLs. Another finding was that ELL-specific training and certification predicted greater Math learning gains for ELL students. While the paper focuses on data from one district, the results illustrate that ELL-specific experiences and training for teachers may help to narrow achievement gaps between ELL and non-ELL students.