Constructivism is a learning theory that states that people learn by actively constructing their own knowledge, based on prior knowledge. A significant number of ICT-based constructivist learning systems have been proposed in recent years. According to our analysis, those systems exhibit only a few constructivist principles, and a critical problem related to the design and use of this kind of systems has been the lack of a practical means to facilitate the instructional design process. Our research aims to help designing truly constructivist learning environments. Our approach is based on a set of operational criteria for certain aspects of constructivism: We use these criteria as a useful pedagogical framework to provide easy-to-use tools and operational guidelines for teachers to build ICT-based constructivist learning environments. One facet often mentioned as being strongly relevant to constructivism is cognitive flexibility. This paper presents COFALE--a new, domain-independent, and open-source e-learning platform that could be used to devise learning conditions fostering cognitive flexibility--and an example of its use: the design of a course on recursion in computing science. (Contains 2 tables and 7 figures.)