We love Singapore Math and use it at home. The one criticism I would make is that we find it doesn't explain new concepts very well. I mean, the pictures are good to visualize this is multiplication, etc. But I just told my son how to carry numbers or things like that.
Second grade is where they need to know their math facts for subtraction and addition. You could also consider throwing in a little workbook on Kumon, which is drill and kill. Just a little since it does get boring but it is very good at getting your math facts down.
I've compared the blue and white version of 2a (I think?) that are more widely available to the equivalent workbook from Singapore Math. They cover exactly the same thing in the same order, and the quality of the problems seem about the same. The major difference is that the Singapore Math workbooks showed the concrete part of the instruction. For instance, in teaching the mental math strategies, the workbook showed the process of what should go through your head. In the blue and white, there was nothing. Same thing with introducing new topics -- the blue and white book by and large just popped out with the new problems. The workbook has just enough in there to demonstrate the concept. It's enough that my DS can often figure it out, and if he can't, I can quickly construct something to help demonstrate the concept that I know will be consistent with the expectations on subsequent pages.
