This text is inspired by the work of Edouard Séguin (1812-1880), a French teacher and philosopher of education generally considered the eminent pioneer of special education and disability studies. It is aimed at lower secondary school teachers (future and in service).

The transition from notions to « ideas » requires links between perceptual notions: for this, Séguin turned to geometry: equal, greater than, composition and decomposition were the starting actions and the comparisons that he proposed to children , using bricks, rods and wooden frames (in a 3D geometry context).

The workshop was organized in three stages and featured the reading of some extracts from his work and a leisure mathematics workshop organized in Spain with children affected by Down syndrome.