This collection of research reports from the Wallace Foundation, Policy Studies Associates, and the RAND Corporation focuses on the development of principal pipelines at six large school districts. The research emphasizes key components of high-quality pipelines, such as job standards, preservice training, selective hiring and placement, and effective on-the-job evaluation and support. The initiative found that the districts successfully established these components at an affordable cost, averaging less than 1 percent of their annual expenditures. Through interviews, surveys, and focus groups, Policy Studies Associates examined the implementation of the effort, while RAND compared outcomes in schools with new principals from pipeline districts to those in similar nonpipeline districts. Schools in pipeline districts with new principals significantly outperformed comparison schools, showing improvements of over 6 percentile points in reading and nearly 3 percentile points in math.