sali You would need to go to your GP with your concerns and ask for a referal to a developmental paediatrician.
You might need to be persuasive so you'll need to think carefully about what, if any of the criteria your ds might fit.
The dx process is a long one and you get to stop it at any point. There are good reasons for getting one and good reasons for not, but if your ds has any traits, for you and him to become as informed as you can will make sure he has the best outcome.
A dx is rarely given if it is not useful, so even if he has traits but they are not interfering with his development, learning or self-esteem then there may well be no point in getting one. On the other hand, a full assessment can mean that the curriculum is differentiated to make things easier for him i.e. if he got stressed in exams etc. and wasted time flicking his fingers, he can be given strategies for dealing with it, take the exam at home perhaps, get a bit extra time etc etc. Or he can be allowed to leave a classroom if at any time he feels he really needs to flick so he can remove himself from the stressful/excitable environment and compose himself rather than behaving oddly in front of his peers.
I'm sorry but my ds is very little so things are very different for us. I would imagine, at 9, your ds will need to consent to the assessment process so you might find it helpful to start a thread asking for people with older children to come forward and give you some information about what books are available for 9yr olds, so that your ds can read and see himself if he can identify with what any of the authors are saying.
I'm not dx-happy, so I hope you don't get the wrong impression from what I am saying. It is just that if there IS anything at all, it is better for everyone if HE and you know about it before he starts secondary school and hits puberty. Quite probably though, it isn't anything, just worth looking into.
Good luck.