I teach special education, and I have had students with these same sorts of issues.  The first thing you need to do is determine the factors that are reinforcing the behavior.  Whenever he misbehaves take a quick note about what triggered it and what happened afterward.  If you notice that he tends to misbehave right before being asked to do work, and that, as a consequence, he ends up in time out (and thus does not have to do work), then you know that the behavior is aimed at avoiding tasks.  From there, you can design a behavior chart.  List three or four specific behaviors listed in a positive manner (do not say, "Don't get distracted" instead say "focus on your work.")  Talk with the student about what sorts of rewards (i.e. a break, a chance to play a game, etc) he would like.  Every time he engages in one of the behaviors you listed, reward him.  Make sure to tell him exactly what he did correctly ("I'm so glad that you stayed in your seat during circle time. Because you behaved appropriately, you may have a 2 minute break by yourself.").  As the student's behavior improves, start using a checklist and giving a reward after he gets a certain amount of checks.
The other thing you have to do is avoid reinforcing the negative behavior.  If he is acting out in order to avoid doing work, then he must do his work, even while acting out.