Understanding place value is key to solving two-digit subtraction problems with regrouping. Illustrate this relationship with a place value mat that has a ones column and a tens column. Use beans, small colored blocks or tokens and paper cups. Place 10 counters in small paper cups to represent groups of 10. Present a problem such a 63 - 27. Place six cups of 10 in the tens column and three single counters in the ones column. Demonstrate how to start at the right, in the ones column, where you have three counters. But in the ones column of the second number, 27, you see you need to subtract seven, so you do not have enough to perform the operation. Therefore, you must take a group of 10 from the tens column by pouring out the counters from one cup into the ones column so you have 13 counters. Remove the seven counters to leave six ones. You have five tens left and can easily remove two to leave three and see that the final answer is 36.
Demonstrate that you can indicate the place value transfer by crossing out the tens digit of the first number in the subtraction problem and writing the next lowest number above it. Write a "1" next to the ones digit to turn "3" into "13" for instance. Let students do a few practice problems, and then try turning it into a game. Put students in pairs or small groups, and give each two dice. Tell them that everyone starts with 99. Students take turns rolling the dice and reading the result as a two digit number. For instance, a roll of two and five can be read as 25 or 52. On the first turn, the player subtracts the result from 99; and on subsequent turns looks at his current number and the roll and subtracts the lower from the higher number. The goal is to be the first to reach zero.
Make a set of matching cards with two-digit subtraction problems and answers on separate cards. Mix up the cards, and lay them out in a grid pattern. Players take turns turning over two cards at a time and solving any subtraction to determine if there is a match. The winner is the person with the most matches when all the pairs have been found.
Story problems sharpen logical thinking skills in math. Give students a few practice problems in decoding two-digit subtraction story problems. For example, "Tessa read 37 books during the summer. William read 68. How many more books did William read?" When students are comfortable translating words to numbers, let them create their own word problems and trade them with classmates to solve.
Computerized math games, whether online or on specialized math software, give students an entertaining and interactive way to practice two-digit subtraction with regrouping. Math Playground's "Thinking Blocks," Mr. Nussbaum's "Draggable Subtraction" or Sheppard Software's "Fruit Shoot Subtraction" are just a few of the options for technology-oriented students to practice their subtraction skills independently.