Educational developers need to assess the work of their Centres, from program participation and impact to underlying organizational processes. Various frameworks exist, but developers may feel unsure how to get started. We developed a planning model that offers a structured, systematic approach for developing comprehensive assessment systems that fully engage Centre staff. The model includes both planning questions and guiding principles, and provided the guidance needed to develop an assessment system in use at one Canadian Centre. Examples from this case are shared to enable others to apply or adapt the model to their own assessment system development.