Effective teachers have an enormous impact on the lives of their students. Great teachers can help students who are behind academically catch up to grade-level expectations. By accelerating student performance, they can help close the opportunity and achievement gaps that cut short the college and career dreams of so many low-income students and students of color. In an ideal world, a comprehensive set of teacher evaluation ratings based on student-assessment data and other measures, such as classroom observations, to answer these questions, could be drawn on. Lacking such data, Education Trust-West used student test scores to estimate the "value added" of tens of thousands of teachers in Los Angeles Unified School District (LAUSD) over a three-year period. It was found that effective teaching makes a massive difference in student learning. However, it was also found that low-income students and students of color in LAUSD are less likely to be taught by the district's best teachers, with teacher mobility patterns and quality-blind layoffs only exacerbating the problem. The key findings are discussed in this report.