DeeDee, this is just my hunch based on what you've written, but I think I'd leave him where he's at now - he seems to be doing really well, he's happy, and it's an opportunity for him to be in a class where he can fit socially, overall it sounds like a good solution.
We haven't ever had our kids take the Explore, so I'm not familiar with scores vs grade level, but I'm curious - when you get a score that is interpreted as "mastered middle school math" - what exactly do they mean by middle school math? That could potentially mean anything from a very basic math course through Algebra II in our school district, which might make a difference in my view of what to do.
You mentioned your ds has completed Geometry in Aleks - where did he start in Aleks? How easy was it for him? Do you feel he's solid in everything that goes into Geometry? Does your ds want more & higher level math at school?
polarbear