I can think of two things I've used in the classroom...one is to say 1, 2, 3, eyes on me (and have him tell you 1, 2, eyes on you) for a quick attention getter. The second is to ask him to repeat what you've just said. Sometimes that helps him focus if he knows he's going to have to tell you it back.
Also, something you might want to ask him when he's daydreaming is what is he thinking about. I had a little boy in particular who was smart, but often daydreaming it seemed. I finally asked him what he was thinking. His mind could not focus...he had so many things going through it at one time. By asking your son, you may get some insight as to what's going on, and it may be something you might want to discuss with your pediatrician if it's overly concerning. Good luck!
at 4:24 AM on Jul. 20, 2008