This report examines whether low-income students are taught by less effective teachers than high-income students and if so, whether reducing this inequity would close the student achievement gap. It also describes how the hiring of teachers and their subsequent movement into and out of schools could affect low-income students' access to effective teachers. The study includes fourth- to eighth-grade teachers over five school years (2008–2009 to 2012–2013) in 26 school districts across the country. Teacher effectiveness is measured using a statistical approach that estimates a teacher's contribution to student learning controlling for students' prior achievement and other characteristics. The study found small inequities in teacher effectiveness between low- and high-income students. However, in a small subset of districts, there is meaningful inequity in access to effective teachers in math where providing equal access to effective teachers over a five year period would reduce the math achievement gap by at least a tenth of a standard deviation of student achievement, the equivalent of about 4 percentile points. The report also finds patterns of teacher hiring and transfers that are consistent with small inequities in teacher effectiveness while teacher attrition is not.