Two-thirds of all computer science teachers in the United States do not have a degree in computer science. As demand for K-12 computer science education continues to grow, and as industry continues to lure computer science graduates away from careers in education, school administrators are increasingly forced to ask teachers with little formal training in computer science to teach computer science courses. This is such a common phenomenon that there are now many competing summer professional development programs aimed at training teachers of other subjects to teach a first course in computer science. However, once these teachers become comfortable teaching the introductory material, there is little support available for them to gain more content knowledge to be able to support their more advanced students or design additional computer science courses. In this paper, we describe our approach to providing more advanced computer science content knowledge to computer science teachers in a week-long summer professional development pro- gram.