Since its inception, New Leaders for New Schools has been driven by the fundamental belief that every child can succeed academically at high levels. New Leaders for New Schools also believes that an effective principal is a crucial lever for school improvement and transforming student achievement at scale. Thus, a focus on the selection, training, and pipeline to the principalship is especially important in the nation's most challenged districts and schools. A rigorous selection process is only the beginning for leadership preparation; it can help to provide an initial diagnosis of strengths and growth areas to focus on throughout pre-service training and into the first few years of the principalship. As all principals know, there is no coursework that can substitute the experience of managing a complex urban school. Aspiring school leaders should work alongside mentor principals to take on genuine leadership challenges such as increasing student achievement across an entire content area or grades and managing a subset of teacher teams. Mentors should frequently monitor the resident's growth and progress toward achieving their project and personal development goals. Similarly, outside coaching should continue throughout a new principal's first year. Aspiring principals themselves must also constantly strive to get better. Not only must they learn how to lead teams of adults and stakeholders; they must also demonstrate a sincere willingness to adopt and implement the practices increasingly known to drive the most dramatic change for their students, staff, school, and community. Rigorous selection criteria and training programs are essential for developing school leaders poised to drive dramatic student achievement gains, but they will mean little without a pipeline of interested and high-quality candidates. A more sustainable leadership pipeline begins and ends with the actual role aspiring principals are asked to assume. School systems will be more likely to attract quality candidates if they are explicit about how they define principal effectiveness and, therefore, what they expect principals to do. New Leaders for New Schools strongly advocates for a three-pronged definition of principal effectiveness: (1) increasing schoolwide student achievement; (2) increasing the number of effective teachers in a school; and (3) taking the leadership actions that will put in place practices proved to improve schools. (Contains 2 online resources.)