Thanks so much for all your replies. They’re very helpful and you all speak a lot of sense. Here’s my detailed response 
@MarshaBradyo He’s in YR6 and yes, I’d like him to be part of the friendship groups from the start
@GolfForBrains the benefit is to have 2 more years of small class size and teaching that we know is excellent, great facilities, there’s no unknown factor plus he has friends there. And yes, I get that it might be hard to get into the state school of our choice and yes, he may have to transfer mid YR8 for that which sucks. Also more hanging round with the uncertainty. This is spot on
@clary yes, I already agree too. Moving in YR7 makes a lot of sense. And I think the curriculum argument you make is very important actually. Time to get into all the new subjects.
@RedGoldAndGreene Unless he mentions the old school by name regularly or something I doubt it will be a problem you're making me laugh!
@RandomUsernameHere Thanks for checking this with your kids. I appreciate it. Luckily though, my son isn’t very posh.
@Clymene Thank you, yes settling in is so important and you also mention the subjects and exams, so glad I asked this question on here actually
@Dontjudgeme101 I’m sorry to hear this about your husband. It’s so sad when someone gets bullied and I’m sure though it made him a stronger person. Yes, a good set of friends is what I’m hoping for for my son
@Oohhhbetty Why would they bully him… I don’t know, because they perceive him as different? And yes, I’d say he is friendly and nice but sadly that isn’t an insurance against bullying? Ohhhh wait, just read your second post now and am taking that back. You actually know a lot about teens and I do remember you from the thread about the recent scandal at DC (and everywhere else, state and private!) I don’t have teens yet and cannot comment on the stuff you’v written but I like it and will keep it in mind. Thank you for the book recommendation too.
@ittakes2 I don't think kids ask each other what school they went to before that’s what I think too! And I guess I’ve written above why we wanted him to stay on in the prep.
@worriedatthemoment That’s right. The reason to stay on is probably not that great
@Firefliess Thank you. I’m going to print out your answer I think. That’s it. He’s changing at YR7 Luckily he plays football
@Cannotgarden had to google that word! I think he’s down to earth, and I’ll remind him also. So sorry to hear what happened to your friend.
@LarryUnderwood Very wise what you say. Thank you! LOL acceptable weirdness.
@balloonsandboobies I guess I wrote above why we wanted him to stay on. I have to admit to leave in what we think is a “bubble” for a bit longer…
@PresentingPercy Yeah, we don’t know if there will be a place…. It’s a big gamble
@SE13Mummy Thank you for summing this up so well.. exactly what we don’t want to happen your DS's final term in his prep school won't be spent getting excited about the senior school he's going to, having visit days etc. but wondering which school he'll be allocated a place at in the July Also the curriculum problems you mention make full sense
Thanks @MrsElijahMikaelson1 Yes, I hadn’t thought ahead with the curriculum choices and GCSEs and so on. Makes absolute sense
@2021Vision Wow yes, I see this now too. We’ll just have to embrace the change this year and not postpone it
@Pupster21 thank you! Yes, I’d hope for him to make some real friends.
@LolaSmiles Thanks for the heads-up with the “Miss” and “Sir”
So how do you address the teacher at state school? I’ll also keep an eye on the middling
@Topseyt Thank you, yes. YR9 is still a time where mostly boys change into secondary. It’s slowly being phased out though
@Firefliess Thank you. You’ve just described our situation and I’m so happy for you and your son that it all worked out. Massive Congratulations are in order. My son has just been through the 11+ and I cannot see him doing this again for the 13+, there’s a few boys like that in his position and it’s sad. I feel strongly that he shouldn’t be pushed to study for another 2 years so that he has a tiny chance to get a 13+ place. Did you have a back up for your son?