Lesson Bank – Mental Math – Place Value in Action

ALT KEY WORDSLike most relief teachers, I love mental math activities as an activity that engages the whole class.

I am amazed at how kids, even the kids for whom learning is a problem, respond to mental math challenges.

This strategy is up there with the best.


Mental Math

Making Place Value Count

It is the cool math skill of adding numbers from left to right and kids love to take on this challenge as the problems becoming more and more complex.

There is an excellent opportunity to scaffold the less capable learners.

They can do a written form of the mental activity until they develop the mental math skills themselves.

This is handy for relief teachers who may not know all student's abilities.

The left to right method promotes a better understanding of place value and the kids see it as a cool math process.

It can be done mentally with much greater ease, and it does not require that numbers be lined up in a column.

Left to right addition involves adding the largest place values first.

As you move from left to right, you keep a cumulative total, so it is simply a number of smaller addition problems.

To give you an idea of how it works and what it sounds like, consider the example, 677 + 938.

Begin by adding the left most place values. In the example this is 600 plus 900 equals 1500.

Add the values in the next place, one at a time, to the previous sum, and keep track of the new sum each time.

Mental Math is Important

mental math activities for relief teachersIn the example, 1500 + 70 is 1570, 1570 + 30 is 1600.

For students who are more proficient at this algorithm, they don't necessarily think "plus 70" or "add 30." Their thought process, if said out loud might sound like, "600, 1500, 1570, 1600, . . ."

Continue adding the values in each subsequent place until finished.

The final steps in the example are 1600 + 7 is 1607, 1607 plus 8 is 1615. The sum is 1615.

As you can imagine, students need to be proficient at single digit addition and have an understanding of place value before attempting left to right addition.

When they are first learning this mental math strategy, they might try repeating sums as they go along (e.g. 1500, 1570, 1570, 1570, 1600, . . .) to help them retain the newest sums.

They might also cross out digits as they are adding.

Why it suits Mental Math.

Left to right addition is well-suited to mental math addition since the sum is cumulative with no steps in between.

In other words, there is nothing for the student to keep in mind except for the cumulative sum.

In left to right addition, the emphasis is on finding a certain place value in each number rather than relying on the place value being aligned.

Students, of course, need to be able to recognize place value before they can be successful at this method. For instance, they should be able to recognize that the ones in the numbers: 514, 1499, and 321 are in the tens, thousands, and ones places respectively.

Place value is a great lesson for relief teachers, as every grade needs this skill.

Learning a wide variety of addition methods allows relief teachers latitude in problem solving situations.

By teaching students this mental math strategy, relief teachers give students another option when they are tackling addition problems.