School practices and policies are often influenced by various research, nonprofit, for-profit, and philanthropic organizations. To help understand their influence, this article provides a framework accounting for the variety of school improvement organizations (SIOs) and summarizes debates regarding their benefits and risks. I cluster SIOs as providing (a) direct school support, (b) research/advocacy, or (c) funding--each with a continuum of organizations underneath them. Studies highlight how SIOs take innovative risks, create improvement networks, and transform school practices. However, they also emphasize the danger of creating challengers to public institutions, the possibility of state retreat, and loss of community input. The article concludes by suggesting ways to use this framework for future studies, assess SIOs' outcomes, and address their risks.