My son is having a really hard time with subtracting 9 and 8. We have used the abacus and he can do it with that but when it comes to mental math he is clueless. Any suggestions would be greatly appreciated. Please help this frustrated mom.
First of all, let him use the abacus until he doesn't need it. I made the BIG mistake of removing the use of the abacus too soon and had to bring it back later because my child couldn't see the abacus in his head. In fact, you may want to consider slowly pulling the abacus away. For example, step one would be to allow him to manipulate the beads on the abacus. Step two would be to allow him to look at the abacus, but NOT move the beads. The third step is for him to move the 'imaginary' beads on an 'imaginary' abacus. The final step would be to have him view the abacus in his head.
Next, there are a couple of games you can use: 'Subtracting Nines On The Abacus', 'Subtracting Nines', Subtracting Eights on the Abacus', and Subtracting Eights'. Instructions for these games are found in the Math Card Games Manual.
You can also give him an exercise similar to the game, 'Repeated Subtraction Solitaire'. Start with a high number for him, like 100 and subtract 9. His answer will be 91, have him subtract 9 from 91, etc. until he can't go any further. If you have a white board or chalk board, I suggest using that as opposed to a sheet of paper. That will make it more interesting for him - at least my kids do better working on the board instead of a 'worksheet'.
I hope that has given you a place to start. If you have further questions or concerns, feel free to email RightStart's help desk at email@example.com.