Thanks for the replies. How I wish I had a copy of Level A to look through! In glancing through the objectives, it looks like my son has already mastered most of the objectives except for subtraction, measurement, fractions, and maybe some geometry. Those topics only cover a handful of Level A lessons, so it appears that it probably wouldn't be worth our while at this point.
On the other hand, there appear to be a few lessons in Level A that aren't in B. For example, Lessons 50 and 51- counting objects by counting 2's? Does Level A do something unique here that isn't covered in B? Also, Level A includes one objective (Can count out 31 objects and arrange in groups of tens) that isn't covered in Level B. Also, it appears that Level A does lots more work with tally sticks than level B- is there some advantage to tally sticks over the abacus for a younger child? So I'm thinking that if Level A is doing lots of different hands-on learning here that is omitted in B, it might be useful for us, after all.

I am just finishing up with level A with my son, who just turned 6. Katie, it sounds like your child is at about the same skill level as mine. We zip through the A lesson in only a few minutes because it is too easy. I then have to expand on the lesson and think up harder problems for him. Level A will ask him to add 40 +2., or 20 + 10. It sounds like these lessons will be too easy for your child too. Most of the tally stick lessons are at the very beginning of the book, and seem to help the child transition away from using fingers. If your child already understands the value of each number then it may be too simple for them.

Hope this helps.

Thanks for the info! I think I will just stick with B and take it slow. I'll just have to simplify some of the existing lessons and probably skip around. I started yesterday on one of the clock lessons and it went fine and we've also been working on some of the calendar lessons. We'll just skip over those lessons that are too complex for now and return to those next year.