This chapter evaluates the effectiveness of a school–university partnership in Erfurt, Thuringia, Germany, called the Network of Erfurt Schools (NES). NES officially ran from 2006 to 2010 as a cooperation between the Erfurt School Supervisory Authority, schools, and universities. NES’s main aim involved contributing to the professionalization of school actors, especially educational leaders, and the development of school organization in terms of development through cooperation at the local level. NES conducted training and offered exchange opportunities. In the area of cooperation, the following elements were promoted: cooperation within the school, cooperative school management, cooperation between schools, and cooperation with other institutions within and outside the school system. The initial focus was on professional development activities; however, during the 5-year partnership, the focus increasingly shifted to the exchange and cooperation between schools in the various areas focused on developing the quality of teaching and learning. Despite its official end as a project, there are still diverse cooperative relationships between the schools involved who continue to work together as a network. The evaluation of NES concludes that there are two main requirements for educators’ professional development networks: (i) integrating diagnostic tools as a starting point for similar programs to identify differentiated needs from which professional development goals/objectives are developed and (ii) a focus on practices to move from knowledge to action. Furthermore, the evaluation offers valuable insight into what works for the development of similar networks: alternating needs-oriented training along with other cooperative options, space for open thought and exchange of ideas, and cooperation between different levels of leadership/management.