I have suggested that you look for a school which strikes you as ‘competitive yet compassionate’.
That is, seek out a school at which your child will find challenging opportunities and where the pastoral care is first rate; a school which knows how and when to temper competition, and where the whole is clearly sub-divided into little battalions. That might well be a school which boasts a clear and effective house and tutorial system. One question you might ask is whether a tutor is actively encouraged to make contact with parents.
I have also suggested that a good school is ‘consistent in its treatment of all pupils’. That is, find the school that takes as much pride in the C grades honestly striven for as it does in the achievements of its top scholars and one at which there is as great a commitment to sport (and music and drama, etc.) for all its pupils as there is encouragement of the self-evident élite. Bad schools take undue pride in the achievements of children who could have achieved all they do whether at that school or not.