This report provides a case study of two authorizers--Denver Public Schools and the District of Columbia (D.C.) Public Charter School Board--both with strong outcomes in many areas and a high or growing charter enrollment. For each, it summarizes how their approach to authorizing has shaped the way they address the issues that arise as charter enrollment grows. It describes how that approach has helped them address specific access challenges. It also identifies the issues on the horizon that will need attention. The case studies that follow draw on nearly a dozen interviews that included authorizers, charter operators, and city-based education organizations and experts in Washington, D.C. and Denver. Although this report includes two cases, it does not compare and contrast the authorizers' methods to draw comprehensive conclusions as to which methods are best. In part, these issues--and authorizers' responses to them--are still relatively new and the long-term impact unclear. [For the executive summary, see ED591850].