Oh dear, what a mess! I really feel for you Crumb. You handled this particular incident badly, but you know you did... You need to work out ways of dealing more positively and effectively with similar situations in future.
But perhaps even more importantly, you all need support with the 'big picture' stuff: understanding what your DS's diagnosis will mean to him, and you. Your 'background levels' of sadness and confusion and stress are probably very high - all of you - and I can't help feeling this will have affected how everyone behaved in this specific situation, and will do again if you don't address it...
How much do you know about dyspraxia? Maybe pop over to the special needs discussion board to chat and find out more... Your son will almost certainly be struggling with all sorts of things; you listed some, but there will be more. Many dyspraxic kids are also dyslexic or have problems with numbers, or both, so you should get him tested. It's an 'invisible' disability, and quite often seems to lead to teasing or bullying, because there's no obvious reason why a dyspraxic kid can't do the things he struggles with. Being bad at team games means he can't fit in with the 'sporty types' at high school, and dyslexia/other learning disabilities mean he can't fit in with the 'geeky' ones, so he could be struggling socially, in and out of school. My DB is dyspraxic, but didn't receive any support with it until sixth form, because he's bright and his intelligence partly 'masked' his dyspraxia. But he struggled with everything at school, and thought there was something 'wrong' with him but didn't understand what, and has grown up anxious and insecure. A proper diagnosis and good support and understanding should avoid this for your DS.
We all worry about our children's friendships, social activities and general happiness. It's hard when their lives don't seem to be going the way we imagined, and we don't have magic wands to make things 'perfect' for them. But happiness doesn't depend on certain magic ingredients (we all know there are rich, unhappy people, for instance) or on avoiding all difficulties, since this is impossible - it depends on having good ways of dealing with difficulties. :)
As for this particular situation, personally I would say this is one of the times you have to hold your hands up, acknowledge you all behaved badly and messed up, and 'start again'. Tell your son you will reconsider the skype ban if he'll talk to you, and then pick a good time for a conversation (car journeys are often good, because there's no direct eye contact and that seems to help teens... But not if you're driving and you know you're going to get upset!)...
Try to discuss the following things with your son. You probably won't cover all of them in one conversation, especially since some of the things you need to talk about will be upsetting... Also, discuss them first with your DH and present a united front if at all possible. You don't need to both sit him down and talk to him together (I think sometimes kids can feel 'outnumbered' by that, and in this situation he needs to feel you're 'on his side'...) but you do need to be sure that if he talks to either one if you, he's going to get the same 'key messages'.
Tell him you handled the situation badly, and apologise. You should never have hit him, you are the adult and should be in control. Tell him - and mean it - that people in your family have a right to feel safe and be safe, and from now on there will be no violence.
If you think that him hitting you and you hitting him was a one-off event that has shocked you so much it will never be repeated, leave it at that. If you think either of you might do it again, then you need some support - start with your GP - because if you do not tackle it now, things will become very serious and dangerous as he gets older and bigger than you.
Don't ask him for an apology. Yes, he 'owes' you one. But you can't 'make' him give one that's meaningful; it's not the words that are important, it's the understanding. You are quite likely to get an apology by the end of the conversation, I'd say, if you don't force one...
Tell him you imposed a punishment when you were angry, and in future you want to take more time and calm down before you punish. (You might or might not also tell him - or at least notice it yourself - that you reacted partly because you had a complaint from another parent: be careful of punishing because you're embarrassed, rather than because he deserves it- it's easily done but not helpful!) Tell him you'll lift the skype ban this time, but he must sit down with you and agree some rules for safe, acceptable use. Tell him you all need to think about these, so you want to do that tomorrow and talk about these other things first...
Acknowledge life must be tough for him at the moment. High school and dyspraxia are both difficult new things to deal with. Tell him he needs to find ways of dealing with stress without using violence, and tell him you'll help him. Ask him if there are other things stressing him out. Don't push him: he may not know what's stressing him out. But if you plant the thought and give him time to reflect, and he believes you'll help, he'll perhaps come back to you in a few days or weeks.
Personally, I would be alert to the possibility that he is experiencing some bullying - perhaps in that specific skype conversation or perhaps not. Don't assume it, but watch out for it.
Acknowledge to him that you're worrying too. Tell him high school and dyspraxia are new things for you, too, and that you are also learning. Tell him you're always there to help him solve problems, and you'll always do your best, even if you sometimes make mistakes. :)
Also help him understand that being bullied and/or being stressed might explain bad behaviour but it doesn't let anyone off the hook! People need to take responsibility for their own behaviour, including their mistakes. Explain that's why you have apologised to him and why you are changing your mind about the skype bad. Explain that he needs to learn to be aware of how he's behaving and how he affects other people, and put things right if he makes mistakes. Ask him if he knows how his behaviour this time has affected you. Maybe also ask him what he thinks he can do to be more aware of how his behaviour affects people... There are no 'right' answers this time - this gives you an idea of how self-aware he is.
Explain your role as his parent is to help him do that... But also that punishments are meant to make him take responsibility if he doesn't do it himself. You're giving him a second chance to take responsibility for his behaviour on Skype, but you won't hesitate to ban him again if he doesn't do that.
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The skype conversation is more practical and less emotional. You'll have your own 'family rules' about time allowed, online security, your access to and checks of his online activity, swearing (or not), bullying, etc. Ask him what rules he thinks are reasonable and encourage him to set his own limits - but don't hesitate to say "No, that's not going to work for me; I say X instead".
This is a mammoth post, Crumb - I hope at least some of it is useful! As a last word, I would just like to say I really empathise with you when you say "I don't know how to give my son a life"... One of the hardest, hardest things about parenting is coming to terms with the fact that you can't 'give' your children a life: the best you can do is support them to deal with the difficulties they face, and make their own lives. :)