The purpose of this research was to explore why some elementary ETS benefited from professional development in terms of increased students' outcomes, while other ETS did not produce the same gains. The aim of this research was to analyze the degree of satisfaction and effectiveness of professional development by interviewing coaches, administrative staff and teachers to ascertain the extent to which professional development influenced the planning and delivery of instructions in the classroom. The area of study was confined to 6 New York City public elementary schools. The study attempted to show the effects of professional development on ETS using School Site Performance as the dependent variable. The findings of this research identified several significant factors to support struggling schools and to turn them into successful ones. The first factor was high quality rigorous professional development, and delivery of instruction by teachers through differentiated professional development. Monitoring of instruction by administration to ensure teachers were on task and were providing standard based rigorous instruction was the second finding. A third finding was that the principal promoted and sustained a culture of collaboration among the staff. The fourth factor cited was that the administrative staff provided resources that were effective and meaningful for the teachers. Finally, data were compiled on every child and utilized to differentiate teaching and learning to address the individual needs of each student. The study also showed that collaboration in the form of inter-visitations among staff, common planning, walk-through, and demonstration of standard based lessons were crucial to the school culture and were embedded in successful schools. The study also validated that the point of entry or workshop model of instruction that was employed as a successful tool for the delivery of an effective lesson. Schools that utilized formal and informal assessment and planned for the growth of students showed increase student outcomes. The findings of this study were highly relevant to the practical positions and roles of assistant principals and coaches. By providing rigorous professional development and monitoring instruction by the administration, the staff improved pedagogically which then translated into increased students' outcomes. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]