A small but growing number of schools and districts across the country are experimenting with personalized learning, an innovation that customizes students' experiences to their individual needs and strengths. Through new kinds of environments, technologies, and ways to demonstrate their knowledge, personalized learning aims to meet students where they are and allows them to advance to more challenging material whenever they are ready. Personalized learning is rooted in the expectation that students should progress through content based on demonstrated learning instead of seat time. By contrast, standards-based accountability centers its ideas about what students should know, and when, on grade-level expectations and pacing. The result is that, as personalized learning models become more widespread, practitioners are increasingly encountering tensions between personalized learning and state and federal accountability structures. Common pain points include year-end summative assessments that focus exclusively on grade-level content, limited end-of-year testing windows, and rating systems that measure school performance based on student proficiency against grade-level standards rather than growth over time. Policymakers at all levels of government appear ill equipped to handle these issues, choosing to avoid the looming conflicts and shying away from existing tools that could be deployed to ease the tensions. This is a missed opportunity. Most personalized learning models are nascent and evolving. They need strong accountability to validate whether they work and enable the best--and only the best--to scale. And personalized learning models could help more schools meet accountability goals, by providing customized learning experiences that fill gaps in students' foundational knowledge and accelerate learning for those who are far behind grade level. The challenge for policymakers is to protect the progress made under the old accountability system while creating space for new educational models to flourish under the next iteration of school accountability. This paper seeks to help policymakers enable smart innovation while also safeguarding the key functions of accountability systems. Understanding the development of personalized learning and accountability--as well as the emerging tensions between them--will help policymakers create accountability policies that complement and support personalized learning approaches rather than work against them.