MagicalMom --- I originally would have said, yes, your son's feet is big for an 11 year old, but I read every one of these posts and I guess my son has average feet (maybe small?). My DS10, who just turned 10, is a size 5.5. And he's one of the tallest in the class.
How tall is your son?
I remember reading an article about kids are getting bigger feet at an earlier age and the average show size is now getting larger.