Deborahf, really sorry to hear about the difficulties you are having with schooling for your ds. I used to work for an LEA and have dealt with SEN and exclusions from that side (albeit a few years ago!), but have also been involved from the parental side when acting on behalf of young people in care. I'm sure you've already had really good advice from ACE, so I'm sorry if I'm saying things that you already know!
Schools should only permanently exclude if there is a serious breach of the school's discipline policy, and if a range of alternative strategies have been tried and have failed, and if allowing the pupil to remain at school would seriously harm the education or welfare of the pupil or others in the school.
Now, if the LEA turned down your request for statutory assessment, that clearly indicates that the school had not exhausted the range of options available to them. Make sure that the Independent panel is aware of this. It would be a good idea to get further details from the LEA about what the school could have done in relation to your DS's SENs and use this in your appeal. It used to be that the LEA had to have a representative at the appeal hearing to give the LEA's view. It would be interesting to see what their position is if they are on one hand supporting the schools exclusion, but on the other hand turning down the request for assessment as the school hadn't done enough to suport DS. LEA's don't always support the school.
Make sure that the information that you want to convey to the panel is clear - obviously these situations are really emotional and it is easy to come to the end of a hearing and wish that you'd said this or that. Do you have to submit information in advance? Make a list of things that you want to make sure are said in the hearing and tick them off as you go along to make sure you say them. If you get to the end and then remember something else you want to say then ask if you can add something - the worst thing is to come away feeling that you haven't made your best case.
You said in an earlier post that if the decision is not overturned then you will face the prospect of having to get ds into another school. The LEA should help you with this. Hopefully your parent partnership officer will be clued up on this. I thought that LEA's have to make provision for excluded pupils after they have been out of school for 15 days - is that happening for your ds? Some LEA's make specific funding available to give to 'receiving' schools to help support the integration of excluded pupils - so definately get the LEA to work with you on that one!
If the outcome of the appeal is that the exclusion is overturned then it would be essential for there to be a re-integration meeting before your ds goes back to set out clearly the support strategies that are going to be put in place for him. Try and get other people involved in this meeting, eg LEA exclusions officer, EP, behaviour support service, so that it is not just between you and the school.
I'm sure that you are currently 100% taken up with the appeal process, but just a quick thought about the request for statutory assessment. When was the request turned down? If it was within the past two months then you can lodge an appeal to the SEN Tribunal. I know that the last thing you want to deal with right now is another appeals process, but the first step to appealing to the SEN Tribunal is just to complete a short form and send the copy of the letter from the LEA turning your request down. You can include further details at a later stage in the process. Given that events have now 'moved on', the LEA may decide to go ahead with the assessment rather than go to tribunal. They may also feel that the exclusion provides evidence that the your ds has SEN's that warrant assessment, even though the school has not done their job properly and done what they should have done.
Sorry this is so long - hope some of it is of use. Best wishes for the appeal hearing.