Any tips on dealing with an anxious child?

My oldest son is almost 11 and he has always been a high stress kind of guy. He worries a lot about school, tardiness, the weather, his brothers, you name it he worries. I have taken him to see a counselor, but that stresses him out too. The change in our family make-up (my recent divorce from his father), has heightened his anxiety. Do you have any ideas for helping this kid calm down? If you were/have an anxious child I would love to hear personal stories.