I'm not sure which we will use. We have 2 and 3 here, and his teacher has 4. He did EPGY Grade 3, but hasn't memorized the multiplication tables (well, he did, but has forgotten them). I hear Singapore Math has a lot of mental math, so I plan to go back through 2 and 3 and review what I think he doesn't know well before we go forward with 4.

I'm sure you've seen it, but here is their placement info: http://www.singaporemath.com/Placement_s/12.htm