Development models often relate expert knowledge to social needs with a top-down approach, thus being not able to cope with the issues of a complex world. Effective changes in social systems arise from iterative and dialogic processes in which information and knowledge are exchanged to build-up a common background that enables shared hypothesis. Therefore the possibility to consciously face social issues and orient the behavior of complex social systems could benefit from the use of communicative tools and methodologies. Engaging complexity calls for visual languages. Based on complexity theories and assuming the interpretation of social systems as systems of communication and learning organizations, a didactical initiative has been experimentally launched in 2004 to answer the following question: How visualization and communication design can be applied to support collective learning processes and decision making in complex systems? After five years of continuous improvements and the development of specific conceptual and operative tools, a didactical framework has been defined with the aim of educating designers in the exploitation of visual languages to deal with social complexity. The potentialities of visualization are experimented in two complementary domains: 1) the visualization of Data, Information and Knowledge (DIK); 2) the visualization of the structure of complex social phenomenon (structural visualization). The paper describes the framework theory and outcomes. The didactical framework proposed here is a multidisciplinary platform, where visual design is the core and leading discipline, successfully complemented by the integration of semiotics, statistics and network science. There are plans to extend the relation and the experimental integration with other disciplines, especially with computer science (evaluating the impact of interaction design in the cognitive processes), semantics and sociology.