If you were to have two students with A*A*A at A Level, one went to a state comprehensive and one went to a grammar they would favour the state comprehensive I believe. This is because you normally get more academic and pastoral help at a grammar than you would get at a comprehensive (not saying all grammar schools and all comprehensives are like this at all) therefore showing that the student at the comprehensive is more independent and hard working. However, people at grammar schools usually get better grades, so it's sometimes the case where you get a grammar school pupil with A*A*A and a state comprehensive pupil with AAB or something. Basically, grammar schools can usually get the pupil to achieve higher grades, which is what universities ultimately want, but anecdotally they would favour the comprehensive pupil if they achieved the same as the grammar school pupil.