6yo DS is fab and groovy, blah blah etc. 
However, some of the kids in his class can be quite aggressive and for some reason he's decided to spend loads of time with them, so he has consequently become much more aggressive and shouty. This will not do! So one of the many things we want to try, to tackle this, is to heavily influence his choice of friendship groups.
He mixes with most of the boys in his class (it's just that he mixes more with the aggressive ones), so I thought I'd start by organising playdates with the nicer kids, in the hope that he gets used to gravitating towards them both outside and in school.
Any other suggestions? Thanks in advance!