I have used many different manipulatives to teach addition and subtraction but this year I came across a really clear way to teach subtraction after just completing a unit on addition. Give each child a measuring tape and use the side of the tape with inches. Have them put their thumb on the first number, such as 12. Then have the students move their other thumb toward zero. They should move the number of inches that they are supposed to take away. This seems to stick with them a little longer than moving blocks, beads or other manipulatives. I think it is because it is one step away - but not so far away - from the concrete.