Teaching material can be time-consuming and difficult to develop, even for those with experience. Teaching repositories permit the sharing of material and can thus potentially save time and enable re-use of good material. Many teaching repositories have been created for this reason, but they often see limited use and we believe there is a missed opportunity to learn lessons and improve the design of repositories accordingly. This paper reports an investigation of the use of the "Nifty Assignments" repository, in an attempt to discern reasons for the success and failure of teaching repositories to enable effective sharing. We go on to discuss the design of a new online community, the Greenroom, for teachers using the Greenfoot environment. The Greenroom attempts to focus on personal interactions and collaborative development of resources in order to increase engagement and sharing, rather than the traditional download-upload models of other repositories. The comparison and contrast of these two approaches reveal interesting insights about techniques which can contribute to the success of repositories