I love speech therapists It seems so unexpected, but it seems they are really running with the challenges presented by ASD's, not shying away at all, and supplying real world solutions. It's not perfect, we're still waiting for them to absorb and teach kid slang (which won't happen, of course), but maybe because it was so unexpected to me, to need that service, I've been impressed.
No experience with the headset and ear piece, but it makes sense to me. One caution is realize your son could find the solution more annoying than the problem, but I don't know how you'd know if you don't try it. Since many classrooms are already set up for speech amplification it probably isn't a huge change to consider.
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Mom to an amazing young adult AS son, plus an also amazing non-AS daughter. Most likely part of the "Broader Autism Phenotype" (some traits).