@Scottishgirl85 A lot of parents choose the grammar DCs friends are going to. Hence you get swings one way or the other.
I have friends who didn’t tutor (plus us) and had very bright dc (not genius level here though!) Others tutored like mad and still dc didn’t get in. Dc felt like huge failures. Money spent that the family could not afford. I would be inclined to practice some tests but doing too much stops other activities. My DD did brownies, Music centre choir & string orchestra, school orchestra, netball and swimming in y5 and 6.
I would say JC take the curriculum at a slower pace but DC do have good opportunities. Also these days, very many from the junior school will go there. Look at their news pages and you see plenty going on. They also report in Wendover News I think. It’s a community school and behaves like one! You would probably have the option of a grammar 6th form.
Obviously there are differences between private and JC or Misbourne but if you might struggle to pay for 7 years, then grammar for 6th form is an option. I’ve not seen anyone I know leave JC though. I would say they are a bit light on hard sciences in the 6th form but you might not have to worry about that. However if you did, that’s a necessary change. Although two dc I know did hard sciences at uni from there.
It’s perfectly possible for academic parents not to have the highest flying Dc but we all
want happy DC. For your borderline DC, you might prefer JC - top of one school is better than being bottom of another which can be stressful - as over tutored dc find out. I’ve seen it lead to bed wetting and school refusal as well as poor behaviour. I’m sure you won’t be that parent, but honestly, JC is fine!