Effective principals are those who boost academic achievement for all students, increase the effectiveness of their teaching staffs, and consistently take leadership actions shown to improve outcomes for students. Therefore principal evaluation systems should place 70% of their weight on the ability of principals to increase student achievement and teacher effectiveness outcomes, with the remaining 30% focused on their demonstration of effective practices and leadership actions. Local school systems should then use these assessments to drive not only key accountability decisions, but also to support professional learning and growth. Bringing significant improvements in student achievement and teacher effectiveness to scale will require substantial improvements in the policies and practices that contribute to the effectiveness of principals. This is a large agenda for change and it can only succeed if individuals accurately and comprehensively measure the effectiveness of principal corps. The goal of this paper is to provide policymakers with recommendations for the design and implementation of strong principal development and evaluation systems. States and local school systems that pursue these ideas can use principal evaluation to drive a powerful vision of principal effectiveness and, by consequence, improve outcomes for all students. Appended are: (1) New Leaders for New Schools Leadership Domains and Key Levers; and (2) New Leaders for New Schools Leadership Rubric Excerpts. A bibliography is included. (Contains 16 footnotes.) [For "Evaluating Principals: Balancing Accountability with Professional Growth. Executive Summary," see ED532070.]