Any chance you could negotiate redshirting him in the sense that he doesn't start school until a year later, but then starting a year up?
That's a great option if you can talk them into it. Even if he starts now, he is likely to find kindergarten boring. However, if it is a half day situation, it might be an easier transition than to jumping into all day 1st grade next year. I think that all day transition is tough for lots of kids.
I find these situations difficult. I know lots of boys held back in our area. All day kindergarten is pretty standard. And I also know several bright boys who were sent after just making the cut off that have had a couple very rough years behaviorally, but are well ahead of the curve academically. I have a son that missed the cut off by about 6 weeks and turned 6 shortly after starting. Kindergarten was great for him socially and emotionally. Academically it wasn't so great, but he did have a creative, open ended teacher. My son was at home and learned so much that year before kindergarten. Looking back, we were "unschooling". A year earlier, for him it wouldn't have great either way. We're homeschooling now, so you can see where that ended for us!
You might want to pursue testing if you really think you need the evidence to get the accommodations and entry you want. Although, not every school will except outside testing. Maybe even ask the school if they would be willing to do testing.
