Student’s modelling with a lattice of conceptions in the domain of linear equations and inequations

We present a student’s modelling process in algebra which consists of two phases. The first phase is a local diagnosis where a student’s transformation of an expression A into an expression B is diagnosed with a sequence of rewriting rules. A library of correct and incorrect rules has been built for that purpose. The second phase uses a lattice of conceptions built for modelling students more globally. Conceptions are attributed to students according to a mechanism using the local diagnoses as input. This modelling process has been applied off-line to data gathered in France and Brazil with 13-16 years old students who used the Aplusix learning environment. The results are described and discussed. The process will be included later inside Aplusix in order to model students on-line and to provide the students’ conceptions to the teachers.