Computer simulation analysis illustrated the thesis that the typical American public school is structured to reinforce students' entry characteristics so that after twelve years, students who entered in kindergarten or first grade with high "readiness" perform academically better-than-average, while students who entered with low "readiness" perform worse than average, creating the "achievement gap." This structure must change if school reform is to be effective. Strong leadership, over time, builds teacher quality and community and parent interest; changes teacher expectations for all students, especially those who are initially and traditionally low-achieving; enhances the quality and intensity of instruction, the closeness of student-teacher relationships, and the rigor of instructional content for all students. These changes result in further advances in motivation, work effort, and academic performance, and finally, improving the school's attractiveness to high-quality teachers, continuing the upward cycle.