This research suggests that London is taking an increasing share of the secondary schools where pupils make the most progress. But places such as Blackpool and Hartlepool (in the north of England) are being left even further behind as debates about social mobility increasingly focus on regional differences.
The study says deprived areas of London can have more high-performing schools than better-off areas outside the capital. David Laws, the think tank's chair and a former education minister, said the widening inequality was "shocking".
But the Department for Education said that its investments in disadvantaged areas would help to spread opportunities more evenly across the country.