High school redesign is one of the most elusive reform challenges to date. This paper explains why personalized high schools are hard to get and keep in a traditional school district, and shows how they can be made much more broadly available through changes in policy and philanthropic investments. Drawing from examples of successful and unsuccessful high school redesign efforts, this paper argues that stable leadership, school-level autonomy, and choice for both staff and families are necessary to support high school redesign at scale. One appendix is included: Impediments to Coherency. Endnotes are also included.