Abstract
Research shows the importance of the development of the learning and teaching of mathematical modelling in secondary school but also highlights some barriers, especially concerning the difficulties of teachers to implement modelling activities. An epistemological study of mathematical modelling and a contemporary epistemological study of modelling experts’ practices led us to identify horizontal mathematization as a crucial component of mathematical modelling. Based on this conceptualization, we then came up with a task for teachers to implement in their classrooms, within a professional development program, which provides us some data to study the constraints and conditions of teaching practices concerning modelling. Our results suggest that a teaching strategy stressing horizontal mathematization is likely to foster a consistent modelling activity of students and that teachers don’t identify horizontal mathematization as a learning issue.