Have you thought of using the students as an example? Like there's a group of 5 students working at this center (use their names), then 2 go to a different center, the restroom, etc., how many are left? You can have them physically get in groups and then have students leave the groups. Hope this helps!
I do not know if you have used this or not, but when I had to teach subtraction to my first graders I used those mini erasers that are shaped like different things such as flowers, ice cream cones, etc. I gave them word problems that dealt with them and had them figure out the answer using their erasers. They loved it and as a little reward you can allow them to keep one or two erasers.
Ring Toss Math
Materials Required: Ring Toss Game, Flash Cards
Activity Time: 20 to 25 minutes
Concepts Taught: to find sums and differences to 18
Divide the class into two teams. Teacher will present a flash card with an addition fact or subtraction fact to 18.
The first player gives the sum or difference. If the student gets the correct answer his team scores one point. The
student is then allowed to toss the ring at the post. If the student's ring rings the post it is called a "Ringer" and
counts for two points. The quieter group, if a difference can be heard wins an extra five points. Exceptional noise of either team
= five points lost. Play continues for a given amount of time. The team with the most points at the end of play wins.
This activity encourages quick recall of addition and subtraction facts. It is an excellent way to make learning of these facts fun.
Have each child in your class make their own abacus for pennies. Then let them use it as they learn arithmetic.
See assembly/directions at: http://www.galaxy.net/~k12/math/abacus.shtml