Thanks so much, MoN and Dee Dee, for your thoughts. This is exactly the type of thing I was hoping to hear about when posting, so don't worry about scaring me. I am not nearly as scare-able as I used to be!
MoN, we are in Fairfax County. I heard about the MoCo program and we considered maybe living there, but I think it started in the later grades, and it would be a really unpleasant commute for DH. Also, both of us lived in Arlington back in single days, so upon moving back (we had moved to Seattle around the girls' 2nd b-day) we stuck with NoVA.
I understand that eligibility may be tough at this point with the school district, based on present levels of performance. We had an IEP in our old school district that was based on their original EI testing, and included full-time preschool with some really nice teacher/student ratios. But even if we were still there, we would be dealing with the triennial now, and I would imagine losing some services.
DeeDee, sorry to hear your DS's K experience. I do think another year of preschool/ABA would be very helpful on the social side. But B is definitely the type to have behavioral problems when bored, so I'm worried the redshirting will actually create more problems than it solves. Also, she is oblivious to all this now (doesn't even know the word kindergarten) but if redshirted she will figure it out someday and that could really mess with her self-image. I am terrified of making the wrong move here. Sorry for going on and on, I really appreciate all you guys offering some help.