Background/Context: Blended learning--a learning model in which online learning is combined with faceto- face instruction to provide a more personalized learning experience for students--has shown enormous growth in recent years. Though many policymakers and educators are optimistic about the potential of blended learning to provide the type of personalized education encouraged by current policy (Race to the Top, ConnectED, etc.), few studies have investigated blended learning in K--12 contexts beyond questions of effects. Purpose/Objective/Research Question/Focus of Study: This qualitative case study examines the execution of a blended school model to understand teachers' roles and practices in that environment. In this article, Cultural Historical Activity Theory (CHAT) provides the framework for tracing how instructional practices and teachers' roles develop throughout the first year of the school and for understanding how contextual factors interact to influence this development. Research Design: This article reports findings from the first year of an ongoing qualitative case study, designed to examine teachers' instructional roles and practices in a blended charter high school. The research team collected a variety of data in order to garner a rich, deep understanding of the contextualized experiences of teachers, including more than 60 observations; two rounds of interviews; and a year's worth of email correspondence, documents, and artifacts. Conclusions/Recommendations: The original vision for teacher practice broke down to varying levels in each classroom, with all teachers exhibiting a return to the pedagogical roles and practices with which they were most comfortable. The tensions, frustrations, and contradictions experienced by teachers throughout the year demonstrate the need for better planning and professional development prior to the full enactment of a new school model, particularly one in which technology plays a large role. For example, administrators and teachers must address how teachers will know that students are using technology productively. Further, because teachers' roles may change in a blended school, these roles need to be defined, and teachers need to be provided with support and training around these roles first, before the students show up. In addition, if an online curriculum is expected to bear the responsibility of assessment and data production, it must first be vetted to ensure that the assessments are rigorous and the data is accurate. Finally, there needs to be planning around how the classroom space should be organized to promote learning, how students will be trained to self-direct, and how teachers will facilitate learning.