"DS is 3.4, he is (I like to think) intelligent. He has a large vocab, knows colours (inc shades) shapes, is very adept with a pc and the internet (for 3...clicking/dragging etc) will happily spend 2hrs or so at a pc telling you about what he's doing) loves playing out etc etc. He's friendly, happy, chatty and polite."
He sounds fine to me If he can sit at a pc for 2 hours there doesn't seem as if there is much wrong with his concentration to me. Also, if he is telling you about the things he is doing on the pc, then I wouldn't have a problem with him spending that time on it. My children can become quite absorbed sometimes on the pc. They don't appear to have been harmed by it and they do seem to learn quite a lot of things. You've also said that he enjoys doing other things too.
"However...His nursery teacher has mentioned that he fails to make or maintain eye contact. He also gets distracted very easily and will become uncontrolably giddy. As one of his teachers mentioned liable to become 'disruptive' He is also liable to bite when tired and run about with his bum in the air, leading with his head on the floor. in addition he will shake his head violently and today he was banging it hard on the stairs."
Is this just at nursery? Perhaps it's a problem with nursery. Does he make eye contact with you and his dad? Perhaps he's not too keen on the teacher. Is he bored at nursery? What is he getting distracted from? Sitting still? If he is fine at home maybe ask at nursery which situations he becomes disruptive in. Could you go in and observe him?
"Today he hit giddiness at home and would not listen to me or DH, ignoring every point we made and continuing with his inappropriate behaviour. In that situation he only seems to respond to a loud voice or sharp tap (and I'm not happy about resorting to that). Thursday he ran across a busy road despite being told to wait patiently. (Thank god for drivers with ABS) That scared the bejabus out of him but only for 24 hrs."
My 3y6m dd has times just like this. As someone else said in these situations we sit and explain to her why it's better not doing what she is doing and if that doesn't work removing her from the situation until she calms down a bit. When it comes to crossing roads I have to grab her and hold her, otherwise she would be off. Being told to wait patiently just wouldn't wash with her, although it has with a couple of my other children. Maybe reigns or something might be a good idea for now. That has worked for me with some of my other children and in the end just the suggestion that I would be putting them on would cause the child to calm down and take note of crossing the road. All mine at 3 were not reliable at waiting to cross the road.
"I am following the school's line of positive disipline so I maintain a continuity of approaches between home and school. I am finding it very very difficult as he sees the 'planned ignoring' as carte blanche to play up. His mannerts have improved no end but....arrggghhh!"
He's 3. It sounds like he's seeing it as a game.
"The Head of the nursery suggested he may benefit from going full time as soon as it can be arranged. They have also suggested an intensive course on the positive behaviour initative."
Perhaps less time at nursery or maybe no time at nursery might be better. Give him time to mature a little bit more and then he might be more responsive when he starts school full-time. Sounds as though he has already learned a lot at home.
"I'm at the end of my teather. He is a wonderful child in all other respects."
He does sound a lovely spirited child full of life.
"I am concerned about his behaviour (my DB had undiagnosed ADHD and I saw the awful affect that had)"
I agree with what has been said before - if you are really worried seek a referral to someone qualified. It will either put your mind at rest or get help for your son.
From what you have said (I don't know if there is more to it - whether you have always had some concerns about him) he sounds normal to me for a 3 year old just a bit giddy at times and maybe a little too young for any formal group teaching.