I think you've left this behaviour rather a long time before addressing it; it will be quite well ingrained by now.
The fact he copes well with school is a good thing. I'd agree with libby, make sure you do the hugging and 'being there', but I think as well as this you've got to try to 'wean him off you' a bit. Don't respond to his demands instantly, let him wait, and then over time let the waits increase. make a point of leaving him, on occasions, but do plenty of loving when you return.
Will he be changing schools at 11? That could completely transform him.