Thank you all so much for your help. My husband and I feel much more confident putting him in the 3rd grade math class, which from what we can tell he knows most but not all of the curriculum. Then we can address if we should do compacted math the following year. We'll continue to brainstorm what the first 30 minutes of his math block will look like, but I'm so grateful for this community who has experience with other "not-so-typical" kids and can offer such valuable advice!