The paper explores the challenges of designing assignments for online learning environments and looks into the use of models as analytic thinking tools for course designers. The paper opens with a discussion on challenges central to designing assignments for online learning environments in higher education. Subsequently, two widely used models for course design, Salmon's five-stage-model (2002, 2003) and Ryan & Ryan's TARL model (2013), are explored with the aim of evaluating their usefulness in Continuing Professional Development (CPD) for teachers and pre-school teachers, a context which has received relatively little attention in terms of research on course design. A number of assignments that have been used in online CPD courses for (pre-)school teachers are analysed with the aim of identifying design patterns, i.e. examples of how recurring pedagogical problems can be solved and, on the basis of this, a new model that can support CPD course designers in designing assignments, the Three Spaces Model For Online CPD, is presented and discussed.