We focus on one of the great current challenges in psychology: interventional research aimed at generating transformation while demonstrating its underlying process. We detail our theoretical and methodological approach and describe an interventional study in the psychology of mathematics education. The psychology of knowledge and our method are based on four connected theoretical aspects: 1. the evidence of interaction between cognitive and social regulations; 2. the role of semiotic mediation in human psychological development; 3. the effects of sign systems on psychological development and individual communication; 4. the realisation that human actions are not at random, but rather content-based social practices. The study involved a double challenge: to develop a procedure to bring a mathematics teacher to a grasp of consciousness regarding the paradigm underpinning her practice, and to reformulate it on the basis of a deliberate articulation between psycho-pedagogical intervention and research, allowing us to: 1. study the students' conceptual acquisitions, and 2. analyse the mediation processes involved in the interpersonal relations, taking into account the nature of the material utilised and the activities proposed. The activities proposed and the quality of the mediated activity meant that students acquired new conceptual competence and the teacher developed new competence as a knowledge mediator.
interventional research; psychology of knowledge; psychology of mathematics education; grasp of consciousness; mediated activity