1. Tell students that they will be exploring how to measure to 100. Ask them to begin the lesson by sharing their ideas about the number 100. How big is 100? How would you measure 100? What kind of object or structure might be 100 big or 100 long?

2. Show students the 100's Day QuickTime Video. Discuss with students some of the different ways that the students in the video measured to 100. Then have them reflect on the same questions they considered before they viewed the video. How big is 100? How would you measure 100? What kind of object or structure might be 100 big or 100 long?

3. Divide students into pairs. Tell them that you are planning to put up a temporary wall to separate off one section of the classroom. You want the wall to be 100 long. Ask students to use one of the materials that you have provided, or some part of their body—such as hands or feet—to mark off how long the wall will be. All pairs should start from the same place (a common wall) to measure the space needed for the new wall.

You may want to provide students with a temporary method for keeping track of their count. For example, if they are using paper clips, they can use a colored paper clip to mark every 10 or 25 in the count. If they are using their hands or feet, they can use small pieces of masking tape or colored sticky notes to mark every 10 or 25 measurements.

After each pair has lined up 100 items, give them a piece of masking tape to mark their end point. The temporary markers can be removed at this time, so the only markers that remain are the end points. Have the pairs write down on an index card which 100 materials they used and then tape a sample or picture of this object (their unit of measure) onto the card. They can then attach the index card to their masking tape on the floor.

4. Bring the class back together and have everyone look at the different measurement marks on the floor. Discuss with students what they notice about the marks. Students should notice that 100 can look very different depending on what objects or units you use. Then discuss the following questions:

1. What would happen if you asked someone else to measure 100 for a new wall? Would they reach the same spot that you did?
2. How would you tell another group to measure 100 so that they would reach the exact spot that you did?
3. What if they didn't have the same materials (or had different-sized hands or feet)?

Lead the discussion to the idea that agreed-upon "units" of measure are important because they tell you what a quantity represents. A length of 100 (or any number) is meaningless unless you know what the unit of measurement is. And in order to have that unit be useful to others, it is important that it is the same for everyone who uses it, whether it is inches and feet or centimeters and meters.