Jumping into the substitute teaching pool with only five hours of training and a salary of $40 per day, Clayvon Harris was determined to make a difference. Instead, she came face-to-face with burnt-out teachers, indifferent administrators and chaotic classrooms dominated by a few out-of-control students who made it nearly impossible to teach or learn. At the end of the school year, she quit with no intention of ever returning. But nearly two decades, four superintendents, three mayors and a state-wide cheating scandal later, Clayvon headed back into the School District in search of a straightforward answer to a deceptively simple question: What's wrong with Philly's public schools?