In many developED countries it’s getting harder to climb the social ladder. In Britain, there is just a 9% chance of a child born in the bottom fifth of income distribution reaching the top fifth. In America, it is 7.5%. The advantages brought by networks, further education, birthplace, cultural references, accent and old-school ties have long been known, but social divisions remain high. What’s gone wrong, and what can be done to level the playing field and increase social mobility?