My student at Houston Elementary used several strategies when attempting to solve math problems. She set up the problems originally using the traditional algorithm that she had seen so many times in the classroom. This is to say that when presented with a subtraction word problem orally, the student would first write on the paper: 7-5=. She recognized that this is the standard form of what I would see on homework or a test. She did not seem to have her math facts memorized, but that did not stop her from using student-invented strategies alongside those taught to her in class to creatively solve multiple problems.
One problem is as follows: John had 13 pennies. He lost 4 pennies. How many pennies does he have now? My student would identify that lost meant that the pennies were removed and that must be subtraction. She wrote 13-4= on her paper. Then she grabbed some of the cube manipulatives and counted out the total number of pennies he started with which were 13. She then removed 4 of the cubes to represent the pennies being lost. Then she counted up the remaining cubes and determined the answer to be nine. She then wrote 9 on her paper to complete the equation.
The student was familiar with the standard form of how we expect children to set up a subtraction problem. For the actual process of finding an answer she used direct modeling with the cubes and counted to find the answer needed. This was just one of several strategies she could have used to solve the problem.
She could have used mental computation. Visual representation is not necessary for all students to solve the problem. She could have counted down in her head to solve the problem. I notice that many students use this strategy with varying results. This is a fast way to solve a problem and is useful because manipulatives may not always be present. The major drawback is the process is invisible to the teacher. If a mistake is made there is nothing that can be referenced to see where an error occurred.
Another strategy that she could have used is subtracting by counting up. She could have started with 4 and counted up to 13 noting how many units were between the two numbers. This is helpful in identifying the relationship between addition and subtraction. This strategy does have limitations when dealing with bigger problems such as 99-23. The thing to take away from this is that there is no one way to solve a problem and it is important to encourage students to use traditional and student-invented strategies to gain a better understanding of mathematics. Counting Up Subtration Model


