This free math tutoring video shows the first way to explain how to do mental subtraction. It is basically the opposite of the way of how mental addition is taught. The next video will show another way to teach subtraction, which may be easier for some problems. Both ways should be taught and children can choose which they like best.
Three manipulatives are shown as options for teaching this concept – plastic eggs, an abacus and Cuisenaire Rods. Feel free to substitute your own manipulatives. The important thing is that the children have something to TOUCH as well as look at when learning how to subtract this way. Enough times of doing it with manipulatives and they will begin to internalize the structure of the method and won’t need them anymore.