Description: Topic : epistemology of educational sciencesConceptual framework: A philosophical and historiographical study of the emergence of new assessment practices inside the French School at the beginning of the twentieth century enables us to understand how school knowledge lost its value, its significance and its central place within the school institution at the very moment, when paradoxically France was emerging as a society based on knowledge and technology. In this process of knowledge transformation, we identify a main step which we interpret as the consequence of both an internal and an external cause, namely Jules Ferry's Compulsory School Act and the classification process that the French society newly expected of its school institution. This step took place within French elementary schools, on the basis of an academic discussion about what an "Abnormal" pupil was and how to identify him.Thanks to considerations related to such an Abnormals' detection, some psychologists led by Alfred Binet developed systematic testing process within schools. However we show that mental tests were not harmless acute and "scientific" tools used to improve classical ways of assessment: they strongly modified the subject as well as the object of the evaluation and also the meaning of these evaluations. As used within the tests, knowledge appears no longer as an aim in itself but as a convenient tool used by psychologists to introduce a sharp classification of pupils according to their abilities.In this attempt of substituting a psychometric-based assessment to a "school knowledge"-based one, Alfred Binet and Théodore Simon performed a dramatic transformation in the field of pedagogical ideas if not of basic school practices of assessment themselves. By inverting the order of subordination between pupils and knowledge, namely by asserting that school knowledge transmission should be organised to be adapted to pupils' own rhythm of learning and not to the opposite, Binet and his collaborators broke the traditional conception of knowledge seen as a self-ordered entity according to which pupils had to be shaped. Along such a reshaping of pedagogical practices and meanings, teachers are less and less "masters of knowledge" and more and more "experts of knowledge", namely it is no longer school knowledge which confers authority upon the "master" who owns it and who has to transmit it to his pupils, but it is "knowledge about knowledge", i.e. pedagogy and educational sciences, which confers an expertise upon the teacher who has to organise a constructivist learning. Purpose: Through the extension of the analysis of the French case to other European school systems, we will study in this paper how knowledge transformations within European school institutions are strongly related to power practices like assessment, and how the competition between various institutional actors induced a reshaping of school knowledge in recent times. Methodology: 1. Historiographical study of materials related to the works of Alfred Binet and his collaborators between 1890 and 1915 and study of materials related to the uses of the Metric Scale of Intelligence in other countries (l'Année psychologique, Le bulletin de la Société libre pour l'étude psychologique de l'enfant, les archives de la commission ministérielle bourgeois, …)2. Epistemological analysis of these materials in a Foucaldian perspective (especially thanks to Foucault's analysis in his lectures at the Collège de France (1973-1974) & (1974-1974)). Conclusions: This paper is intended to be an epistemological contribution to the understanding of the mechanisms of knowledge production and transformation within European school institutions.