99% of grammar schools are good or outstanding. 75% percent are outstanding. They provide excellent education and are oversubscribed.
There is already a wide range of published research that explores the question of the effect of grammar schools on social mobility.     
In order to promote greater social mobility, the Memorandum of Understanding (MOU) between the Department for Education and the Grammar School Heads Association sets out the commitment of its members to increase the number of disadvantaged pupils on roll. Many prioritise pupil premium children for admission. Those gaining places in a grammar school will benefit from the high quality education they deliver.
Alongside the MOU, the 22 successful bids from the Selective Schools Expansion Fund all prioritise pupil premium children for admission, with some also committing to lowering the entrance test pass mark for such pupils and undertaking outreach work to increase the number of disadvantaged pupils on roll. They are in the early stages of delivering their five-year plans.
 Andrews et al., 2016, EPI, “Grammar schools and social mobility”
 Atkinson et al., 2006, "The result of 11+ Selection: An Investigation into Opportunities and Outcomes for Pupils in Selective LEAs"
 Gorard and Siddiqui, 2016, "Grammar schools in England: a new approach to analysing their intakes and outcomes"
 Burgess et al., 2018, "Assessing the role of grammar schools in promoting social mobility"
 Cribb et al., 2013, "Entry into Grammar Schools in England"