peer reviewed ; Several recent studies about school mobility highlighted the significant decline of active modes and public transport's modal shares. Associated with this decline, it can be observed that distances between home and schools have been rising the last two decades. To develop appropriate policies alleviating the negative effects of the increased motorization in the school commute, a diagnosis of probable causes is required. To perform this diagnosis, we develop an accessibility-based methodology using data stemming from the Belgian national household travel (BELDAM) survey. Gamma-functions are calibrated to describe the use of different transport modes according to their relative travel times. Data from OpenStreetMap are used to describe the Walloon roads network in terms of the maximum allowed vehicle speed and length for each link. Properties of the network are modified to match with other transport modes. Maps of accessibility to schools are computed for each transport mode by merging the value of access time represented by isochrones and the calibrated gamma-functions.