I think too many people mix up what constitutes a good education with exam results. The two are not really linked!!
Education is about providing a well-balanced human being who is confident and comfortable in a wide range of situations, someone who understands the viewpoint of others in society, particularly those less lucky than themselves, those from more difficult backgrounds. It's about being able to see the world from multiple persepectives. School have a role here, but the vast majority of education in life, both academic and non academic comes from parents. It's parents who teach their kids the vital skills necessary to enable children to do well in school from reception class. It's parents who teach tolerance and understanding of others. Travelling is well known to be one of the most beneficial ways for a child to gain education in life. You can always tell well-travelled kids (and I'm not talking about those who go to Ibiza to the beach), kids who have experienced different cultures, these kids just have a worldly-wiseness about them that stands them in good stead for life. A good school supports all of this.
Fundamentally if a school supports all the above paragraph sadly none of that will show in exam results which are pretty easy to fix and fudge. Anyone who judges a school on exam results needs their head testing frankly. Far more important is how the school looks after the welfare of the children, how they deal with the more vulnerable kids, the pastoral system, the ethos of including everyone not just the bright. For a school to excel at this it needs a wide range of kids - it's this that provides the vibrancy that kids need to blossom.
As for the best school in Stafford, value added is far better measure of attainment than 5 A-C grades percentages. Some schools only enter a kid once, and are open to accepting that their kids might not get the best results, but they haven't spent 3 years learning how to pass an exam, they've been educated to ask questions, to be a good human being in the modern world. It's important to know how many kids are on free school dinners, a good indicator of children from more difficult backgrounds, how many are special needs. A good school includes these children and they thrive but it usually negatively affects the schools over all poition in the league table. i know which kind of school I would prefer my child to go to.
Is Walton the best school in Stafford based on these criteria? Not in my opinion, nowhere near. Is Stafford Grammar with it's narrow social intake? Again, not for me. Balfour, King Eddies and Weston Road all provide a far more balanced and inclusive education for all their kids, where everyone is welcome, not just the kids who will do well in the exams.
If your kid is really bright and academic attainment is the most important criteria for you, then Adams and Newport Girls piss all over Walton in the league tables