We are using the 3rd edition and some of the extra challenges. Those are fun.
Right now we are doing the time chapter, which he needed some work on. He knows his facts quite well. He is very fast with addition. Subtraction still needs a little bit more speed, but we are working on it. He always gets it right though.
He already know how to add with renaming (or carrying) up to 4 digits. We haven't yet done subtraction with borrowing, but I know that it is something that he will pick up quickly on. His forte is actually computation. He picks up on it quickly. The spacial concepts are his harder portions.
Looking ahead in the 2nd grade book, what he hasn't really learned would be subtraction with borrowing, intro to multiplication and division (though division is just briefly covered), and a little bit more complexity with geometry (vertices and such).
I always felt that during 1st grade, it was moving slow. Now 2nd grade seems the same way. IMO, he knows about 50% of the material already. About 1/3-1/2 of the remaining material are topics that he picks up on easily and I was wondering if just the review section at the beginning of 3rd grade would cover that.
I really don't feel like I am pushing him at all to advance. I actually put him back into 1st grade grammar because that is not his strong suit and he was struggling early on. But math is his thing. He sees patterns to it all the time that I think are really neat (my DH and I are both math-y people too). Right now I am giving him each chapter test and seeing if there is a portion of it that he is struggling with. We go over that and skip the rest.