I was in the same boat with DS5. So I just jumped ahead to LOF Fractions. I didn't like the idea of starting at the beginning, no matter what, and I think the author's recommendation of going back to the beginning, if you finish, is a little ridiculous and only aimed at making more sales. That said, Fractions was a good place for US to start, and I see no problem with having missed the earlier ones. In fact, there is still so much stuff in these that is review. So, go ahead and jump, without following author's recommendations. I don't have advise on which one you should start with, but you really don't NEED to read all of them for them to make sense. They seems to be over-heavy on filling you in on what is going on. And as others on here have said, these aren't a complete curriculum - just some fun math filler. After doing the Fractions book, we aren't going to be getting any of the others - but I am glad we tried it and I do think it was worth it.
