International audience; The school quasi-market in French-speaking Belgium is characterised by segregation of various types. Efforts to apply measures that encourage greater social mixing have met with stiff resistance and various difficulties. In 2008 and 2009, a significant amount of turbulence was caused by the application of the "social mixing" law influencing the registration procedures for students in secondary education. 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, the foundation of the quasi-market mechanism. To do this, a generalised formula for allocating funds to schools according to need is proposed on the basis of legislation currently in force in the French Community of Belgium. 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 of schools according to these indicators are presented, through simulations using real data on the effects of these scenarios in terms of gains and losses first for all schools, and then for different contrasting schools thereafter. 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.