Is he supposed to have a water bottle at school? I don't know if this would work for him, but for our extremely sensory dd, sucking on a straw satisfied the same type of sensory urge that caused her to chew. We also got the OT end-of-pencil chewie things that look like erasers when she was your ds' age. She ultimately grew out of her need to chew, and I will never know *exactly* why it happened, but I think that it was due to addressing her sensory needs in larger ways (she went through sensory OT, listening therapy and we did a lot of brushing/joint compressions) combined with identifying and reducing the things in her environment that ramped up her sensory needs (in her case, vision challenges and anxiety-producing situations).
Best wishes,
polarbear
