Six years on, this very laudable idea has now evolved into an American initiative, Let Girls Learn, which Mrs Obama discussed with David Cameron at No 10 after another school visit in east London. There are 62 million girls in the world who are out of school: the US and Britain are now launching a partnership to help change that, starting in the Democratic Republic of Congo. The statistics show why this is such a good idea. As well as being morally right, educating girls leads to greater prosperity; it leads to lower levels of maternal mortality and Aids; and as Mrs Obama has argued, educated girls are one of the best weapons against violent extremism.