We did really well for a month, completing through lesson 15 of Level B. Then some things came up and we took three weeks off. Now my son understand the concepts like adding on the abacus, etc. but he no longer quickly recognizes the number represented there without counting beads individually or singing the whole "Yellow Is the Sun" song.

Is there an idea besides drilling to help reinforce this? We can do that a little but he will get bored of that quickly at his age!

Have you looked through the math card games book? In the number sense section at the very beginning I know they have a lot of different games using cards with tally sticks on them, or two hands with all the fingers or the abacus beads. There were different matching games and things to play with them to recognize them. I'm in the process of moving so I can't look through mine (I just packed it!), but I know there were some games and in the back were the cards that you just photocopy.