This is a case study conducted in a preschool organization in Sweden. The study is based on the problem of how the organization of collegial development work in preschool can be improved and developed so that it leads to a real and lasting change in pedagogical practise The purpose of the study is to identify success factors in the organization of collegial development work at the preschool. It’s done with the help of the research questions "How has the preschool organization in a municipality chosen to organize an initiative of collegial development work?". and "What factors for successful and sustainable development work can be identified within the organization?".   Several levels in the organization were studied. The study was conducted through qualitative interviews with nine informants: the head of department, two principals and three employees. In addition to the interviews, documents produced by the principals and supervisors which are linked to the collegial development initiative were collected. The interviews and documents were analyzed through thematic analysis and coding. The results of the study show how the organization organized a development work and what success factors were identified through the development effort. Several success factors were identified, such as leadership, mapping to identify the need for the development effort, a culture and group dynamics that support change and development, that there is a local connection so that employees understand and are motivated to drive change, and that there is space and time for a collegial development effort. The conclusion is that there is no given and simple way to organize a collegial development work, there are several different parameters that come into play, although the study finds some common success factors that are highlighted as important for the work to be successful.