Use money to teach regrouping in subtraction. Saxon Math, a recognized leader in math instruction, suggests a visual approach to regrouping. Use play money in both $10 and $1 denominations, and teach students to trade a 10-dollar bill for 10 one-dollar bills so that they can perform the necessary subtraction operation. Point out to students that now they have fewer 10-dollar bills because they have traded one.
Teach place value first: ones, tens and hundreds. Students need to have a good grasp of place value before they can understand that one 10 is equal to 10 ones. Houghton Mifflin, another heavy hitter in the education world, recommends students write out the numbers in a subtraction problem in expanded form to more easily move tens into the ones column.
Use manipulatives to demonstrate regrouping, using different colors to represent ones, tens, hundreds and so on. If you use red for ones, blue for tens, and black for hundreds, students can trade one blue for 10 reds. Having enough reds now, the student can subtract. This approach is both visual and tactile, allowing students to see the trade and to work the subtraction with their fingers by removing the ones that are taken away. Math manipulatives are available at educational supply stores and online. If you don't want to purchase manipulatives, you can substitute pony beads in different colors or other small objects.