In this paper, we present some results concerning an assessment practice, composed of oral interaction between a teacher and students that a mathematics teacher, Jose, in a context of a collaborative work, uses to develop the capacity of self-assessment of his secondary school students. The assessment practice developed by Jose includes two ways to promote self-assessment: self-assessment of the answer and self-assessment of performance. While the former is ensured by cognitive and motivational strategies, the latter is mostly based on meta-cognitive strategies.