Sorry to hear about this. It isn't your fault - it can be a good choice to "stay in the background" at times. It is still early in the year.
Can you talk to son and get some sense of his perspective. And what sort of behavioral issues and what is the plan to address them. They may or may not be linked to boredom, you know his history in that regard. But it worthy of more investigation.
Do they do any pretesting to find out what your child already knows. Can you arrange for it?
My response to the "all kids end up even up" is to smile sweetly and say, "yes that does happen eventually if you don't bother to teach the ones that are further along anything new." Warehousing isn't just a term that applies to the education of special needs/developmentally delayed.
Good luck and keep us posted.
Cat