We are about 3/4 of the way through Level B (started at 5, she is now 6). My daughter was doing well but when the addition progressed to double digits and then to mentally adding double digits (L 76, L 80), it was too much for her to do on her own and I was somewhat surprised.

I think it is usefull to look ahead in the Table of Contents where you can see related concepts to get an idea of how things will progress and when you can see the concept advances, that might be a clue that by that point, the child needs to have mastered the supporting skills.

Hope that helps.

I' doing RSB with my 1st-grader, and just switched from Singapore to RSC for my 3rd-grader. The two-fives strategy is covered again in RSC, along with a practice sheet, so don't worry if it isn't "mastered" in first grade. Two-fives is only one of many addition strategies they will learn, and it may not be their favorite. If your kids can't see it yet, let them use the abacus. Make yourself a note in future "warm-up" lessons to add a few "two-five" addition problems using the abacus. For example, you enter 7 + 8 on the abacus and have them tell you the whole equation. Do a couple of those with each lesson, and soon they'll have the strategy.

Double-digit addition I also thought progressed very rapidly. I started asking the questions like this: What's 65 + 20? [85]. What's 85 + 7? [92]. What is 65, + 20, + 7? [usually a long pause before answering 92]. So what is 65 + 27? [92]. I might reduce the number I ask every day if it seems to be too much, or bring out the abacus and have them talk through adding the tens first, then ones.

Keep with the theory of "scaffolding". That means providing just the support necessary to help your kids along to their next level of ability, always letting them do as much as they are able. A building can't be build higher without scaffolding around it, and our kids can't learn a brand new concept without a little help and pracitce... every child learns differently, so don't be afraid to tweak things a little if yours needs a little more than the teachers guide gives.

But I also like that the concepts cycle, so don't worry if they don't get everything this time! Blessings!