From the posted references it appears that the Investigations material is seriously defective as a math course. Perhaps it could be used to supplement Singapore Math or something else, but not the other way around.
I would definitely agree with this statement. There are certain investigations in the geometry and fractions units that I absolutely love, and I use some of the conceptual number activities as warm up or for independent activities, but after trying to implement it as core curriculum for a couple of years, and watching my children bring home work from the curriculum in the earlier grades, I consider it to be dangerously incomplete.
The more time I spend with the Singapore Primary Math curriculum, the more impressed I am with it. I will use it as a core curriculum for the first time this year and use Investigations and other sources to supplement and in some cases pre-assess conceptual understandings. That said, I will still post-pone teaching the standard algorithms until I can verify a certain level of mental math ability with groups of students. I will definitely postpone fraction work until I am confident that students actually grasp relative size and meaning of fractions. Those particular area have been critiques of the Primary Math curriculum that I have found valid for students who don't have good number sense. However, those critiques have led to a throwing-the-baby-out-with-the-bathwater response to Primary Math which I find to be both illogical and foolish.
