The school quasi-market in French-speaking Belgium is characterised by segregation. Efforts to apply measures that encourage greater social mixing have met with stiff resistance. In 2008 and 2009, turbulence was caused by the application of the "social mixing" law influencing the registration procedures. The purpose of this article is to present some results from a prospective research project that investigated the possibility of modifying the formula for financing schools. To do this, a generalised formula for allocating funds to schools according to need is proposed. Then, the solution tested is presented with a financing formula that takes into account indicators of the social composition of the school population. Various scenarios of differentiated financing are presented, through simulations on the effects of these scenarios for all schools. Finally, the implications of these scenarios are discussed and put into perspective with respect to the different solutions considered since 2005 in French-speaking Belgium. (Contains 7 figures, 6 tables and 19 notes.)