This article investigates how a computer simulator for human interactions and a dyadic system in a pencil-and-paper environment can contribute to helping students with poor motor co-ordination, notably those with dyspraxia, to learn geometry. The aim is to design an alternative way to teach the subject, and to explore its effects on the learning processes. Geometric construction is an important element in the curriculum in primary and secondary school, but is not an end in itself. We draw upon Efraim Fischbein's work, in particular the link between the figural and conceptual aspects of geometric objects, in order to design a simulator that can execute geometrical constructions for students with motor co-ordination problems, who find drawing difficult. Our initial experiment with students with dyspraxia and their peers showcases the potential benefits of alternating human--human and human--avatar dyads. It serves as a proof of concept and highlights the way in which students appropriate the artifact and construct an instrument in the context of drawing.