This book presents the results of a four-year, National Science Foundation-funded project that engaged nine high school biology teachers at three public high schools in long-term, on-site professional development program centered on a learning progression. It explores the influence of teacher participation in this professional development experience on their learning about student thinking, formative assessment task design, classroom practices, and student learning. Taking an in-depth look at the multiple sources of data gathered as part of the study, this volume reflects on the emergence of professional communities focused on formative assessment design and enactments and associations between teacher participation in learning progression-centered professional development and student learning.