The best science teachers are not only experts in teaching and knowledgeable about science content, but they are also great at teaching science. They have specialized teaching knowledge, including knowledge of effective pedagogical practices in science, student difficulties with understanding content, and curricular purposes. As a result, professional development that is both content-specific and anchored in what teachers must do in the classroom is becoming the norm for helping teachers improve their science instruction. Less widespread is professional development that prepares teachers to design units of instruction for students by using available materials or developing their own lessons. This may be in part because some education leaders and researchers do not believe teachers have sufficient skills and knowledge to design instruction for students, so they focus on preparing teachers to follow curriculum developed by subject-matter experts. But teachers inevitably do adapt curricula and programs to fit their classroom contexts. In their work, the authors have found that content-specific professional development that prepares teachers for principled adaptation of curriculum has potential for improving student learning. In this article, the authors describe the comparative teacher and student outcomes of three content-specific professional development programs that were tested in a school district in Florida. They also examine costs that districts may want to consider in selecting a professional development model to adopt.