Get on the bus with your son, sit a seat or two behind, witness the bullying and report the incident to your sons school and that of the bullies.
If you have to step in dont give yourself up as his parent as this may attract further attention, if it becomes too much get involved and come across as a concerned "do gooder".
Remeber when it first starts you will want to steam right in but let it go for as long as possible and dont loose your rag, easier said than done but the more info you have the better.
(camera phones are a great invention)
Continue onto the school to which they are attending and report the incident imediately to the Headmaster along with a list of other times and dates that this has happened.
That way you can give a full detailed description of the twats and they will more than likely be hauled out their class and told to report to the headmaster.
Tell the Headteacher that you will be reporting this to the police and that you want to be kept informed of his actions, if you are not happy with any thing you hear notify him that you will be involving the local Education Department for Glasgow it's Nye Bevan House, 20 India Street GLASGOW G2 4PF
here is a list of local education depts
http://www.scotland.gov.uk/Publications ... 5640/12180
Next contact the local community policeman/woman and involve them it'll send a rocket up the schools arse in terms of you taking it seriously.
They will in turn contact the school to which these idiots belong to and also speak to the powers that be.
We had a problem with our 10 year old being harassed by 13-14 yr olds at the bus stop, I done the above and was initially advised by the school that "could she perhaps not get a later bus" aye right!
I done the above and now we dont get any bother.
Or
Get him down the gym and intae the boxing.
B.