I tell students that today they will be rounding to the hundred's place . I ask them to think (silently  2030 seconds) about the strategy for rounding to the ten's place will be applied to rounding to the hundred's place. We have discussed this before but it's important, so I bring up this connection repeatedly. They may write down their idea in their journal and then share with a partner before I call on them randomly on several students to share out to the class.
Alternative questions:
What will you do that is the same as rounding to the ten's place and how will rounding to the hundred's place be different?
**What do you think you will have to watch out for? (common errors)
I draw several open number lines and review how to round to the closest hundred for the following numbers. I also call on volunteers, in this case, to demonstrate, especially for the values less than one thousand.
53 
89 


148 
250 
772 

1,556 
2,443 
3,450 
4,689 
12,124 
64,980 


I am explicit in the use of the terms digit, number, one's place, ten's place, hundred's place, thousand's place, tenthousand's place. Again, I emphasize that the tens place is the key to determining which is the closest hundred.
The students and I use open number lines to solve how to round to the closest hundred.
Colossal Fossils is a short guided practice activity in which students will be rounding various types of numbers (dates, ages, number of prey animals) to the closest hundred. This practice is embedded into simple expository text about a few animals that both lived in the Cretaceous period and whose fossilized remains can be found in some of the clay formations of Alabama and Mississippi. The questions in the guided practice can easily be answered on whiteboards or scrap paper or, if you prefer, on this Colossal Fossils Guided Practice student page. If you use the student page you will see that there is room on the bottom half of the 3rd page for students to take notes, using two of the icons from Sandra Kaplan's Icons of Depth & Complexity as an organizational tool. I explain that, briefly, in this short video about the Details and Language of the Discipline Icons.
Also, if you prefer just the math content without additional reading/science questions, here is a math only version of the guided practice PowerPoint and the accompanying student page:
Colossal Fossils (math only) (ppt)
Colossal Fossils Guided Practice math only (student page)
Students work to round numbers to the nearest hundred and are expected to explain (spoken) their strategy.
Possible groupings:
On/above level students could work on Colossal Fossils Independent Practice individually, with a partner, or in a small group.
Students who would like to work on just the skill of rounding, without extracting the math problem from the context of fossils, could choose this page: Rounding to the Closest Hundred (Math Only)
If student work from yesterday shows the need, here is a short video clip that reviews how to round to the closest hundred. It could also be viewed by a small group of students during the (optional) differentiated portion of the independent skill practice. It also may help students to be introduced to or review the idea of using place value block representations to think about the value of the number in the tens place and whether to round up to the next hundred or down to the existing hundred.