I like Zaccaro's Primary Grade Challenge Math. I also like Venn Perplexors and math material from The Critical Thinking Co.
I second the suggestion regarding Penrose the Mathematical Cat. We started reading it last week and it seems like a great fit for DS5 right now.
My mathy DS5 likes to play Descartes' Cove with me. He needs help but he is fascinated by it and learns a lot of math from it. I think of it as a fun teaching tool.
It makes me wonder if it would work for my mathy DS5. He works on 4th grade level, but I think Descartes' Cove is 6-8th grade. Let me know how it goes. If your son stays with it for a few months I may consider it too.
