Although the terms scale and scalable are often used in the context of Open Online Education (OOE), there is no clear definition about these concepts from an educational perspective on the course level. This paper critically discusses the origins of these concepts and provides a working definition for educational scalability. A heuristic framework, which integrates four common educational design principles, is introduced, in order to study support and formative assessment and feedback at large scale. The proposed framework is presented, discussed and applied to five case studies. First qualitative results of the case studies show that the designs are relatively similar. The detailed study of their units of learning, however, indicates practices which can potentially be interesting for other MOOC developers to enhance their design and their scalability. Further research will apply the framework to zoom in on scalable best practices in MOOCs with a focus on scalable practices of formative assessment and feedback.