Choose a visual aid. This should be an item you have identical copies of, preferably 10 or more, such as note cards, playing cards, pieces of fruit or cereal pieces. Tell the learner that each item is equivalent to the number 1.
Set up a visual subtraction equation by placing, for example, four of your visual counters on a flat surface. Place two more of the counters to the right of the first group, leaving space between the two groups. Place a page horizontally above the counters. Write the equation 4 - 2 =" on the page so that the numbers and signs correlate to the visual representation. Have the learner fill in the answer.
Ask the learner to consider the visual equation. Point out that each of the two items in the second group is being subtracted from the items in the first group. Tell the learner to pick up one counter from each group and set it aside, then ask him to repeat the process. Point out that this is subtraction.
Ask the learner to consider the number of items remaining in the first group. Note that these two items are the result of the subtraction and thus can be moved onto the other side of the equal sign. Ask the learner to count the leftover items and write the result into the equation that you wrote on the paper. Point out that the learner has just completed a subtraction problem.
Repeat Steps 2 through 4 numerous times. Use different numbers each time. Once the learner can easily and consistently perform the visual subtractions, write new subtraction problems to be performed without the visual counters. This will ensure that the learner has grasped the concept of subtraction, as opposed to simply counting the items.