Why invest in your neighbor? Social contract on educational investment

It may be in the interest of low-ability individuals to subsidize theeducation of high-ability individuals. The sufficient conditions aresurprisingly mild: positive externalities in education andcomplementarity in production between human capital and labor suppliedby the low-ability individuals. However, tax competition and the freemobility of the educated give rise to time-inconsistency and free-ridingproblems which render such a social contract infeasible and result in asuboptimally low investment in education.