I'm sure I've found useful parental contributions on TSR, on Mumsnet and on other sites.
Regarding 'context' and Oxbridge applications, my understanding is that everything is taken in - and decided upon in – context, both ‘deprivation’ type indicators and other factors. It can even vary for two very similar applicants in the same class at the same school. In real life it's often very difficult to find out and unravel what is formally 'context' and what is something else.
In January 2016, there were two girls in my daughter's class for one subject, girls from very similar backgrounds. Cambridge told the school their applications, including the tests, were very similar. But they offered one AAA and the other, for the same degree course, was offered AA* AA. Was doing 4 A Levels part of the broader consideration? Or was it just unmoderated subjectivity and lack of consistency across the 31 colleges’ 31 different subject Directors of Studies and 31 different Admissions Tutors?
Pragmatically, I would expect all Departments at all Universities to contextualise everything and, I’m afraid, there will also be variation and subjectivity from candidate to candidate, from course to course and from year to year.
By the way, I think Oxford centralises more and moderates better than Cambridge at the moment.