I agree about the fractions in Singapore Math, Taminy. My son already had a solid grasp of what they are before we started with Singapore Math, and I could see value in different types of clear models and hands-on exploration to make sure that students got the concept before really digging into the work. In fact that goes for a lot of early topics, including multiplication, division, etc. I really think that good-quality "Investigations"-type modeling and discovery might make a good addition to just about any curriculum, actually. It could always be slotted in during the introductory period on that topic. I just don't think sole reliance on that approach would be good.
In my local school district here in New Hampshire, they seem to take that approach to some extent, and it's one thing I like here. They begin with multiplication, division, and fractions all at the same time in first grade, long before any emphasis on learning times tables, doing pencil work with long division and the like, etc.
