The IFS report on this, pretty much sums up my position on grammar schools (there is also plenty of other research into the effects of grammar schools and it all points to much the same): "Grammar schools seem to offer an opportunity to improve and stretch the brightest pupils, but seem likely to come at the cost of increasing inequality. Inner London, by contrast, has been able to improve results amongst the brightest pupils and reduce inequality. This suggests that London schools probably offer more lessons on ways to improve social mobility than do grammar schools." We know what works and it isn't grammar schools, which bring down attainment levels generally, increase inequality and don't actually offer the brightest anything more than the average inner London comprehensive.