Development in the domain of mathematics from birth through the end of adolescence generates increasingly more complex, abstract, and rule-governed concepts, and more versatile, flexible, and planfull problem solving skills (Demetriou, in press). Nothwithstanding major work done by developmental psychologists and mathematics educators like Baroody and Dowker (2003), Hiebert (1986), Rittle-Johnson and Siegler (1998), Star (2005), and many others,..., the respective roles of procedural and conceptual knowledge in students’ learning of mathematics continues to be a topic of animated debate. A related topic of great theoretical and educational importance that still has not lost its importance since Piaget’s pioneering work, concerns the relationship between (the development of) mathematical knowledge and (more) general cognitive processes and constraints. Recent theoretical and methodological developments, with important implications for both research and practice, have led to new approaches to these two topical issues. Compared to previous research, this recent work is characterized, first, by a greater reliance to longitudinal and intervention methods that seriously take into account the impact of people’s instructional histories and, second, by the use of more advanced and sophisticated methods and techniques for data gathering and data analysis (including brain imaging techniques, structural equation modeling, to mention just a few examples). The present symposium comprises four papers of original research programmes addressing the above pivotal issues, followed by two discussion papers, one by a developmental psychologist and one by a mathematics educator.