I have Singapore 1A/B and RightStart A. Both rely a lot on regrouping, number bonds, and other strategies for imparting a more conceptual understanding of number and operations, not just memorizing math facts. I think both programs have their strong adherents. It's just a matter of finding the program that suits your child's learning style, I suppose.
I was sure that my ds would love the manipulative-based, game-oriented, oral approach of RightStart. We both
hated it. I don't think I can emphasize that strongly enough.

Each lesson is heavily scripted, and I just could not get used to teaching that way. Even though I tried just reading through the text so I could present the lesson in my own way, the activities, graphics and manipulatives just didn't do it for ds. Each lesson also presents several different topics, and that style doesn't suit ds well.
I know there are legions of RS fans out there. Our experience was pretty disappointing. And since we bought all the extras, it was an expensive mistake.
I am currently taking more of a living math approach, but I supplement occasionally with Singapore, Miquon and MM. We love Singapore, and I think the HIG does an excellent job of presenting different instructional strategies for each lesson. Ds loves the workbook. The presentation of the math concepts make sense to him. I realized that while he does like manipulatives and games, he much prefers to be able to work out math problems on his own, without the dialogue that is intrinsic to the RS approach of doing math. I know Math Mammoth is also touted to present math in a very student-friendly way, but ds is a very visual learner. The MM graphics (or the lack of them) was a dealbreaker for ds. MM also has sooo many practice problems. Too many for my ds. Singapore and Miquon have been our favorites, without a question.
Since you are asking about Singapore, I like having the HIG, the textbook, the workbook, and the Intensive Practice book. There are lots of folks who don't "need" as many, but I found that each book gives a slightly different approach to presenting different math concepts. I like being able to select from them. Singapore does a nice job of laying out the number and operations lesson sequences. Singapore gives lots of different strategies for learning math facts, so while the drill and memorization are not built into the practice problems so much, the opportunity to learn math facts thoroughly is there. I am less thrilled about their lessons on money and time, but we take a living math approach with those concepts anyway.
And since you are also taking a LM approach, I thought I would mention that we also really like the activities in the
Week-by-Week Essentials. Tons of printable math games, mental math problems, math warm-ups, etc. They help to round out our math program when we do some of these activities along with our other mathy activities.
I am also thinking about how I can implement a math notebook with my very reluctant writer/drawer. The ideas are percolating, but we aren't doing anything consistently yet.
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