Fast forward several decades, and I became the fourth grade teacher. The traditional strategy just didn't seem to help my students "get" rounding. I wanted my class to understand that rounding involved finding the closest multiple of 10, 100, 1000, etc.
Let's eavesdrop on this week's class discussion:
- Me: What is rounding?
- Student: It's sort of like estimating.
- Me: Why do we round?
- Students look around and act unsure.
- Me: Let's say I go to the store with $50 in my pocket. I want to purchase three items. One item costs $19, another is $11, and the third is $13. I want to make sure I have enough money when I get to the counter to pay, so I round each amount then add to see if it's more than $50. I use rounding to figure out about how much each item costs (in this case to the nearest $10) then I add them together. That final step, adding rounded numbers, is estimation.
This year I've decided to have students take notes for each concept. Here's our page for 4.NBT.A.3:
Next I modeled rounding the number to the nearest 100; 1,000; 10,000; and 100,000. After demonstrating with a few more numbers, they worked some problems with me, and finally they set off on their own.
This year we'll use rounding a lot! As students review longer addition and subtraction problems then learn long multiplication and division, I will require them to estimate. In fourth grade, students will estimate on paper, but in subsequent grades they should be able to estimate mentally. This arms them with a powerful tool! Estimation (which is addressed in 4.OA.A.3) allows students to know if the answer to a complex problem is reasonable (or if a red flag is being waved), and it allows them to go to the store with $50 and figure out if they have enough money to buy a series of objects.