Hi Deborahf - just a thought before your planning meeting next week, and please don't feel that I'm telling you what to do or how to act - it's just my opinion!
I've found in meetings like this that schools can be really really defensive - after all, they've basically been told very publically that they did not act properly, so it's an understandable reaction. The worst thing that can happen is to dwell on what the school didn't do as this can result in them not wholeheartedly working with the re-integration and setting him up to fail so that if they go down the exclusion route again they will be making the point that they were right in the first place - if you see what I mean.
Be really positive about your DS going back there (after all, the school should see your appeal as an indication of how much you want him to go there). Emphasise how much your DS wants to go back, so despite the difficulties he's had there he must have had some positive experiences. Acknowledge that there have been difficulties but keep to the perspective that you're not looking back - the re-integration is about moving forward.
What's really important is to find things that will be different when he goes back, so the school don't think that they are in the same situation as before - if nothing's changed then what's going to make things different this time? For example if the drug treatment is having benefits for your DS that could be it, if other agencies are going to become involved then focus on that, if the statutory assessment is going to begin then that's another thing. Do you see what I mean (it's late on Sunday and I'm past it!).
What I'm trying to say is to focus on the positives, acknowledge the difficulties and emphasise the things that will be different when DS goes back.
I've been to meetings like this that can start out a bit defensive, but by the end can be really positive having worked out a plan to support a child.
I really hope your meeting goes well, and again I hope you don't think I'm interfering!