Constructionist learning is when learners construct mental models to understand the world around them. It advocates student-centered, discovery learning where students use information they already know to acquire more knowledge. Students learn through participation in project-based learning where they make connections between different ideas and areas of knowledge facilitated by the teacher through coaching rather than using lectures or step-by-step guidance. wikipedia 
See Seymour Papert
More than a theory of learning, constructionism seems to be how brains work.