Hi Colleen. At some point yes because when giving people their change back this is the way you and them know that the right amount is being given to them. This is also the quickest and easiest in the long run. At first is this necessary? No as long as your son understands what he is doing and you know he "sees" what to do. It's great that he is using the abacus to figure out these money problems. I would invite him to consider counting it up. Have him first figure out what the change would be. Have him lay that out in front of him. Have the original amount he was given out in front of him as well. Write out the amount of the item and have that out in front of him too. Now model for him by pointing to the amount owed and then to the coins that represent the change. Do this a few times, then ask him to do the same. You may have to start it out and have him repeat after you. You can also show this on the abacus as well. Please do. My son had a bit of difficulty transitioning to counting change up but he did get it and actually enjoyed it in the end.

I hope this helps.

Sincerely, Rosine