The Literacy Lab Professional Development provided a laboratory approach to professional development for 42 high school teachers in two schools. Three main activities included: (1) planning and professional development days, (2) lab and professional development days, and (3) individual coaching. The targets of the Literacy Lab Professional Development and its associated guiding questions focused on student engagement and understanding, teaching students how to make meaning from text, teaching students to write, and the structures, systems, routines, and rituals needed to create a classroom culture of thinking and learning. Results from this study point to positive differences between participating and matched-nonparticipating teachers in their instruction, student grouping, nature of tasks, task demands, types of knowledge expectations, personalization, tone, and authority structures.