Professional development in science education aims to support teacher learning with the ultimate goal of improving student achievement. A multitude of factors influence teacher change and the effectiveness of professional development. This review of the literature explores these factors and identifies school and district science leaders as a critical factor missing from current professional development models. School and district leaders play a significant role in the planning and implementation of professional development, as well as providing ongoing leadership to support teacher change. Considering this role, school district leaders are not just a contextual factor, but rather an integral part of the process and should be integrated into and considered part of any professional development model in science education.