There is growing interest, worldwide, in collaboration between schools and community organisations in contributing to and enriching school science programs, yet such collaborations are inadequately understood. This paper reports data from an Australian study designed to probe the views of members of the community who have participated in a broad range of such collaborations in school science programmes in order to better understand the issues which impact on their operation. The data were collected by interviews with the community participants selected by opportunistic sampling. The analysis reveals a number of issues--purposes, communication, organisational structures and curriculum--which can be seen as impacting on the collaborations. These are examined through the concepts of communities of practice, boundaries and boundary crossing, associated with people from scientific communities of practice interacting with school communities. The paper reflects on the implications of these findings for constructing effective school-community collaboration in school science programs.