Add me to the list of moms who think this could be a sensory issue. My son never chewed on shirts, but his own fingers, metal objects, and occassionally other children. He also has sensory processing disorder and constantly needs oral input, especially when stressed. His OT got us a couple of chewy tubes, which work well, but are expensive. A speech therapist suggested the tubing, and it works just as well, is cheaper, and easier to replace when lost. If your son has an OT or ST, ask about it; otherwise, get him evaluated by the school district. Be aware, however, that not all OTs have experience with sensory processing disorder. I'm a teacher and I've run into a few that work for school districts that have no training in it. Good luck!