[stanley]

I have the same problem. As I teach children of expats, I also have some near native speakers of English in the same class as children with very little English at all. I am currently working out how to deal with it. To get round the problem, I intend to do a lot of group work and have the children mainly working in same-ability groups. For those with limited English, I will try to simplify the task so that the language I want them to use is at their level. I wouldn't worry too much about a 6 month difference. I would do as simplyesl suggests and make sure you review previous language all the time, in warm-ups and games. (I'm sure you do this anyway, so sorry if it sounds obvious) In my experience, even when classes are grouped according to ability, there will always be a range within that and you may well find that some of your new students are quick learners and will soon catch up with the majority. Good luck!