hi~
it is difficult to stop a "habit" or "behavior" without replacing it with something else. Since your son is old enough to talk to about this ask him what he thinks about his habit, if he knows when/why he chews on his shirt (BUT do not make him feel guilty or ashamed that he does this), if he wants to change his habit and tell him that you can work with him on trying to replace the habit of chew on clothing with something else. Also come up with a cue with him to remind him when he is chewing (since it is very likely unconscious) – a word such as “gum” or a silly word like “bananas” – or a tap on the shoulder.
When thinking about what to replace it with try oral activities. Provide these “oral” experiences frequently throughout the day such as:
* chewing gum
* in school (or homework time, etc) possibly try using a chewease pencil topper -- http://www.pacificpediatricsupply.com/cart/index.php?main... FYI - if you use this see how he does. you may need to remind him to swallow his saliva so it doesn't get caught up in the tube.
* during meal times try krazy straws, drinking thicker drinks from straws (such as apple sauce, fruit smoothies, etc)
* use sports bottles
* play blowing games (e.g use a straw to blow cotton balls across the table – you can set up “goals” worth certain points)
hope that helps – good luck!