Dyslexia is a medical category recognized nowadays within education as an institution. This paper shows how, in France and the United-Kingdom, with the success of the category of dyslexia since the early 2000s, social relations are taken into account less and less in the dominant and most legitimate representations of educational issues. Firstly, the category is part of the power relationship between scientific disciplines; what is at stake is not only the production of knowledge but also the ability to act within society through the school system. Secondly, the current ways of thinking, as well as measuring devices, contribute to making dyslexia an a-social problem.