This Rounding to Nearest 10 & 100 PreAssessment is a quick way to get a big picture view of how the class as whole understands the concept of rounding and where I need to start. It also gives me the information I need to plan informal groups for differentiation.
After this lesson is over, I go back and look at each student's preassessment. Here are a few student examples (note  I had my students complete this on lined paper instead of the printed sheet). I use this and their work from class to gauge their placement/ need for support or enrichment in tomorrow's lesson, Rounding to the Hundreds Place. Additionally, if the majority of the class needed extra support at this level I would continue this lesson another day before moving on to Rounding to the Hundreds.
While the lessons here are listed as one day lessons and one hour lessons, it's important to know that I would repeat or extend them depending on the needs of my individual class.
The two essential components of rounding are:
I directly teach the following examples to give students the chance to practice finding the midpoint, something they often don't know how to do. As I draw the number lines, I explicitly talk through each step. I count up to the halfway point by ones, mark the halfway point, and reiterate that from that halfway point on we round up to the next number. Depending on the needs of the group I might teach fewer or more examples than those listed below.
Halfway/midpoint (rounding to nearest ten)
160 and 170 
400 and 410 
740 and 750

1280 and 1290 
2620 and 2630 
3370 and 3380

11,250 and 11,260 
49,810 and 49,820 
88,050 and 88,060

Based on what I observe during the guided practice, I give them one of 3 short practice pages on finding the halfway point. I collect them and look at them after school to determine who needs extra help during the next lesson.
Midpoint Between Tens (extra support)
Midpoint Between Tens (on level)
Midpoint Between Tens (above level)
Remember, finding the halfway point between two given numbers with values such as 600610, 12201230, 14,500, and 14,510 is a deceptively simple task. When rounding a number, students need to be able to do two essential tasks. They must be able to accurately identify the preceeding and following ten AND they must be able to accurately identify the midpoint between these numbers. For them, it is an abstract, twostep process and one with which they need specific, straightforward practice.
After we've practiced identifying the halfway point, I reteach the skill of finding the ten before/after the number they are given to round.
I directly teach counting down and up to the closest ten for the following examples because I have found some students do not identify the closest ten. For example, for the number 234, some students may identify 210 and 240 as the closest tens.
35, 87, 265, 430, 1287, 2455, 94,211 Based on what I observed during the guided practice, I give them one of 3 short practice pages on rounding to the closest ten. Those who need additional help work on Rounding closest ten extra support, those who are on level work on Rounding closest ten on level and those who have already demonstrated complete mastery of what we've done so far work on Rounding closest ten above level.
Even after all these years of teaching, it can take some reflection to determine the best way to build in support. In this instance, the videotaping was very helpful to me because after school I was able to reflect on my conversation with this student in order to come up with a better plan to meet his individual needs. In his case, handwriting is very laborious, so simply providing him with a template instead of having him draw it out, or having him write just the answer when we worked through number line problems together, ended up facilitating the learning process.
This is conceptually difficult for some students so at the conclusion of this lesson I remind them that knowledge and skills are not acquired instantaneously and reassure them if they are worried that they "don't get it" yet.