Are there any end of the year paper/pencil assessments they can give him? Our district had a completely unreasonable acceleration policy, in that they wanted the child to score 98 percent accurate for material up to the point that they would be accelerated to. Current school is much more reasonable (I think it's 80 percent--so DD, for instance, is now in 5th grade and if she scores 80 percent on the end of the year assessment, she can skip 5th grade math). My DS was given the acceleration assessments when he was in first grade (at the school where they wanted 98 percent) and I think he was very unfocused. There was a whole category where he was clueless (measuring to cm with a ruler) so of course he didn't get the 98 percent. I argued that I could teach him to measure with a ruler in about 3 minutes and it was ridiculous to hold him back for a couple little gaps like that (I said it more nicely than that, but that was what I was trying to get across), but i may as well have been talking to a brick wall. He did the WJ ACH as part of his IEP eval and scored 155 for broad math which put him at around a 4th-5th grade equivalent, and they couldn't have cared less. They also had his IQ scores. It didn't matter.

Luckily he is now at the school which is not so rigid (they just require the 80 percent) and he is in third grade but will be sent to a sixth grade classroom for math. He also was saying that he hated math, and now he says he loves it. He says that the rest of school is a waste of time, but he could sit in math all day.
I would ask about having him tested on their own measures. Sometimes I think tests like the WJ are meaningless to them, plus so many mathy kids in the K and 1st grade level seem to get sky-high scores if they already know multiplication, division, etc. Good luck.

Singapore Math has paper/pencil (short answer and open-response) end-of-course assessments for each half-year (available as downloads on the www.singaporemath.com website), for which they specify 80% as the minimum mastery score.