Subtraction is a difficult concept for students to grasp if they are uncomfortable with place value. Once way to assist students in being successful with the place value in subtraction is to introduce them to place value "houses." Students start by drawing three houses in a row, which represent the ones house, the tens house and the hundreds house, etc. Throughout the lesson, the teacher should refer to the "houses." Students will be reminder that any math problem begins with the "ones" house.
Students will understand the concept of subtraction (especially when regrouping) if they are able to visualize something. One way to do this is to encourage students to think of the bottom number as people and the top number as apples in a tree. This visualization technique will remind students to start at the bottom and look up to see the apples for correct subtraction. If there are not enough apples in the tree for the people on the bottom, the students must go next door to the tens "house" and take one of the tens and add it to the apples to have enough for the people on the bottom.
Base 10 Blocks are an essential manipulative that teachers can use to help teach vertical subtraction.
When introducing the concept of subtraction without regrouping, teachers use Base 10 Blocks to represent the numbers in the problem. For example, with the problem 55 - 32, the child lays out 55. Looking at the ones blocks (also called units) the student takes away 2 units and writes the number of the remaining units (3) in the ones column. The student then moves to the tens and takes away 3 of them. The students then writes the number of remaining tens (2) in the tens column.
Using Base 10 Blocks when regrouping is a more difficult concept, but with practice students are sure to grasp it. For example with the problem 34 - 18, the student lays out 34. The student is then directed to try to take away 8 ones. There are not enough. Teachers will guide students to discover where they can get more. By taking one of the tens it can be exchanged for 10 units. Now the student can take away 8 ones and write the remainder, then take away one ten from the 2 tens that are left. The answer is 16.