The National Institute of School Leadership's (NISL's) Executive Development Program (EDP) was established to provide professional development to school leaders to drive their schools to high performance. The program emphasizes the role of principals as strategic thinkers, instructional leaders, and creators of a just, fair, and caring culture in which all students meet high standards. Its primary goal is to ensure that the participating school leaders have the knowledge, skills, and tools to effectively set direction for teachers, support their staffs, and design an efficient organization. The curriculum is organized into four courses: "World-Class Schooling" (Principal as a Strategic Thinker and School Designer, Standards-Based Instruction), "Teaching and Learning," "Developing Capacity and Commitment," and "Driving for Results." Training sessions are designed to be highly interactive through the use of simulations and assignment of "pre-work" and "homework" to participants. This study examined the impact of EDP on student achievement in Pennsylvania schools from 2006-2010. It updates and extends a prior evaluation (Nunnery, Ross, and Yen, 2010a) study of this same cohort from 2006-2009, which found that elementary, middle, and high schools served by EDP principals had significantly larger gains in the percentages of students achieving proficiency in reading and mathematics. (Contains 1 footnote, 9 figures, and 4 tables.)