This paper seeks to highlight the weight of the personal component (Robert & Rogalski, 2002) on the professional development of teachers engaged in two research-training experiments on assessment practices in mathematics in primary schools. Professional development is understood through the evolution of elements that constitute the evaluation logic of teachers. To study it, we convene the framework of the theory of activity reviewed by Engeström, which makes it possible to highlight the mediation tools and rules called for in these two research-training experiments.