Dear Sarah,
You can give him one or two as part of your daily warm up. Also, there are several math games that use this skill. A64 Column Addition and A65 Repeated Addition Solitaire are both great games. Also, the Chain solitaire games help with just basic addition as well as the Corners games. All these will help keep his skills current. The more he plays, the more mastery of the basic facts he will have.
Nancy

Thanks for the information on the games. This is a big help. Because RS B is so scripted, it can be hard for me to break out of the mold for reviews and practices. I find myself keeping checklists of what my kids need review on/more games--what they still are not getting even when the lessons have moved on.

I would like to say that I have been very pleased with RS B. My son LOVES math and his mental math capabilities exceed mine.

Dear Sarah,

As you probably know, Lesson 90 is preparation for Lesson 91, where the child discovers for himself how to add 4-digit numbers without the AL abacus. I have found that children making that discovery and doing the six worksheets don't forget it. The beauty of truly understanding is that "maintenance" is rarely an issue.

The topic is revisited again in the next level.

Joan

Thank you for your reply, Dr. Cotter. I am looking forward to learning more with my son when we do Level C. I am very grateful for this curriculum. You seem to understand how children think and learn!