There have been lots of posts on this in the dim and distant past, but I would reiterate what other people have said. Nonsuch and Sutton Grammar perfectly doable from Kingston, though still requiring a reasonably early start. You could get the 7.30 X26 from Kingston and should still get to school on time. The 213 is sooooo much slower through Kingston/New Malden.
Wallington Boys unfortunately is a different matter. Once you're on the X26 its easy but you would have to get the 7.00am bus from Kingston which could mean leaving home 6.45ish depending on how your DS would get to the station. Personally I think that's very early but some do it. My own DS does get that X26 but he's able to pick it up further down the route and it gets him into school before 8.00, but he quite likes that (plays table tennis in the playground.) We looked at the later bus (which is scheduled to arrived at WCGS on time) but it pretty much never runs to schedule - and I actually followed it in my car on a couple of occasions just to make sure
He's also lucky enough to get a lift to school a couple of times a week so we decided that the commute was doable and in his words "It's not that big a deal." Although the first few times he had to get out of bed at .645 were interesting....
Personally I wouldn't touch Wilsons with a barge pole from Kingston, certainly not on the bus anyway. You would end up having to get the early X26 and then changing to a 154 from Carshalton. I'm not aware of anyone who does that though there probably are boys who go by tram from Wimbledon. Lots of changes of transport though and I think that's where the commute gets stressful. All you need is for one of the links to break down and it doesn't make for a happy journey.