I read as far as the part about constructivism and then I jumped to the end. Sorry if I'm just repeating what others said, but I wanted to say that I ordered all the new elementary Life of Fred books for DS5 and he absolutely loves them. However, I don't know whether I'd use them as a curriculum, but they're a great supplement, and DS loves the quirky stories and humor. Truth be told, some of the subject matter is far below his ability, but because of some of the math concepts and vocabulary to which he's not otherwise exposed and even non-mathy concepts covered in each book I decided to get all of them. The stories make the stuff that is review for him interesting enough that he doesn't seem to mind. I think depending how much work you wanted to do you could create lessons that expand on the material covered in the books, or you could use them as a way to figure out which things your child needs to work on more and skip the things that they don't.
