Like many other multi-step 3rd grade skills, rounding numbers in 3rd grade can be extremely complicated. Rounding requires so much attention to detail that its purpose is often lost in 3rd and 4th grade.
Rounding in one strategy that can help students make reasonable estimates when adding and subtracting in 3rd grade. It receives a lot of focus because it involves so many different details, but rounding should always be tied closely during instruction to estimation.
MA.3.NSO.1.4 I can round 2- and 3-digit whole numbers to the nearest 10 or 100.
Rounding to the Nearest 10
Even though students first start rounding 2-digit numbers to the nearest 10 in 2nd grade, starting with this skill is a great way to introduce it in 3rd grade as well. 3rd graders are developmentally better prepared to work with rounding as a strategy for estimation because of their more advanced number sense and place value understanding.
The basic concept of rounding to the nearest 10 is that every number is located between two tens. The two tens are the endpoints – the number will be closer to one of them. Since 5 is midway between the two tens, and equidistant from them, a rule had to be made about which way a number that is the midpoint will round. The rule is to round numbers with 5 ones up to the next ten, but that is also the least accurate rounding scenario. That means when working with midpoint numbers and estimating for addition or subtraction, a different estimation strategy might work better (be more accurate than) rounding.
Students should have plenty of early opportunities working with smaller numbers and rounding to the nearest 10. Number lines are the most-used rounding strategy. Working with base-10 blocks or digits on place value mats and number charts will offer another perspective to help students master rounding. Incidentally, rounding to the nearest 10 is almost always the most accurate place to round whole numbers to! The intervals between the endpoints are much smaller, so the span of possible numbers rounding to the nearest ten is much less than rounding to other places.
Rounding to the Nearest 100
Introduce rounding to the nearest hundred to 3rd graders with 2-digit numbers. They need to shift their thinking from intervals of 1 to intervals of 10 on their mental number lines. That means they will now focus on the digit in the tens place to round to the nearest hundred. The rounded estimate will have zero tens and zero ones. Like I mentioned earlier, there are many small details to pay attention to! Learning to round should not be a rushed process so students can become comfortable with the concepts at their own pace.
When rounding to the nearest 100, the endpoints will be hundreds and the midpoint will be 50.
Again, the midpoint will be the number that is least accurate when rounded to the “nearest hundred.”
A number line with 10 intervals between hundreds endpoints will be numbered by tens instead of ones.
The ones exist in the tiny intervals between the tens.
Rounding to the nearest hundred is usually far less accurate than rounding to the nearest ten. For example, the midpoint for rounding up to the nearest 10 is 5 intervals from the upper interval. The midpoint for rounding to the nearest 100 is 50 from the upper interval. Students learning to round should also be developing an understanding of accuracy.
Since we estimate for different reasons, different levels of accuracy are appropriate in different situations. 4th graders will soon learn that rounding to the nearest hundred is usually far more accurate than rounding to even higher places!
Standards
Rounding is in every major set of standards in the 3rd grade, but their levels of rigor are not consistent. The Common Core Standards don’t specify the magnitude of numbers 3rd graders should be working with, so educational resources vary significantly.
The Texas Essential Knowledge Standards currently have 3rd graders working with 3-, 4-, AND 5-digit numbers, which is higher than both Common Core and Florida’s B.E.S.T. These higher expectations have 3rd graders locating numbers between 10s, 100s, 1,000s, AND 10,000s!
This is a rigorous goal for 3rd graders but does give them more experience with larger numbers before the 4th grade (when numbers get HUGE!). I also appreciate that TEKs includes in operation standards rounding and using compatible numbers to estimate solutions. Without this language in standards, other estimation strategies besides rounding can be ignored.
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