The goal of this article is to present and theorize our more successful and less successful attempts to create and sustain problem-solving forums, in which exploratory discourse takes place. The main argument is that many implementation-related phenomena that we have encountered when working with seven high-school classes for one or two school years can be characterized and explained with the aid of conceptual tools provided by Rogers' Theory of Diffusion of Innovation. The most successful process of forming an online forum in one of the classes is presented in some detail, and the parallel processes in the rest of the classes are presented in the form of an aggregated summary. Implications for future design-based implementation research are drawn.