sugarplum I suppose it might vary by state and even rural/ urban area, but where we are it is very nearly impossible to send your child to any state primary school other than their catchment one - its different at secondary, but I have never heard of anyone changing state primary except by moving house.
Mixed aged clubs with a sub set of children they are at school with can be good though, helps them belong more... Its good when they are with children older than themselves too because then those children are also vaguely looking out for them at school. That's what we've found to date anyway. But of course also good to have friends from elsewhere. Karate could well be a good one. We have found football to be the making of DS1 though - he was cripplingly shy for a while but the whole team nature of football and the fact they train together three times a week gave him a real group identity - he's been with the same club since he was 4 (so for over 5 years now) and they really have each other's backs. Its not for everyone though - my DS2 tried it for a bit, but he isn't really a team type 
tbh I'm not either 
but for children it suits it is brilliant.
Bertie be careful to "read between the lines" of everything you are told and see at open days at the free school - the Eltern Initiative Aktive Schule I taught at was also a free school and there was indeed more proactive involvement in solving conflict, but there were also more behaviour problems and more bullying than at the state Grundschule as far as I can see because they had such a concentration of "Square Pegs" - a very tiny school which very naturally appealed to those whose kids weren't fitting in for all sorts of reasons, or indeed were on last warnings for behaviour, at state Grundschule in the area, including several who had been through 5 or 6 state and private schools already by the age of 8 or 9 ... There was a higher concentration of difficult characters than in the general primary school population and an awful lot of time was spent with all the children sitting in a circle talking through conflicts and proposing resolutions, which seemed a good idea but did not always/ often actually achieve much once a day, or an hour, had passed...
A bigger, long established school may well be entirely different, but it would be a big reservation for me, about sending children to that sort of school.
When I do crossing patrol at our Grundschule once a fortnight I am also unofficially watching the playground for that hour before school starts, and yes there are some scuffles, but so far calling out the kids' names has always broken them up, and then kids who feel vulnerable will tend to stand by me (and on other days whoever is doing crossing patrol) at the traffic lights until the (church) bell chimes 7:45 and they are allowed in.
They aren't as micro managed as in England but I don't think they are bad kids for the most part - knowing their names and who their parents are as far as possible helps :o
DD glided through Grundschule without any conflict at all, so it does depend on the child and boys do tend to have a different experience I think (not by their intrinsic nature obviously, before anyone assumes I mean "boys will be boys" :o but that does seem to be a general trend for whatever sociological reason...) I must say DS1 has been generally unruffled by conflict he has been caught up in personally, and remains quite a sensitive type who gets upset at any and all perceived unfairness and so, ironically, gets himself involved when he could walk away...