This guide from AI for Education presents guiding questions, key steps, and strategies for developing a schoolwide GenAI policy. As many PreK–12 schools and universities explore the affordances and tensions of GenAI use, this guide offers useful tools to engage in critical dialogue about student and faculty use, ethical concerns, and academic integrity. The guide recommends a collaborative approach to policymaking between students and teachers that involves a common understanding of GenAI and a set of guidelines about usage, citation practices, and data privacy. It also calls attention to ongoing concerns about GenAI use in schools, such as AI issues with hallucinations and implicit bias, and with user overreliance. The guide concludes with strategies for introducing policy to different audiences, including interactive activities that allow both students and teachers to gain an in-depth understanding of the policy.