To begin this lesson I wanted to provide students with an opportunity to create and use a variety of rulers. Doing this will allow student to connect their prior understand of non-standard units learned in previous lesson.
I ask students to move to their assigned seats. I model how to draw an open number line. I explain that number lines can also be used to measure. Can someone tells me what tool this reminds them of? Ruler You are exactly right! Now I want you guys to create your own number line. Since I drew the first model, I show them an example of a ruler.
Before they began to draw I point out to create their number lines with evenly spaced points. (Please demonstrate for accuracy.) For struggling students I give them some tiles to help determine an even amount of space.
After students are finished, I tell them that we will be using rulers to help us solve addition and subtraction problems to 100. Some of the student recognized the similarities between a number line and a ruler. However, some students were unable to recognize the similarities. One of the most common misconceptions is when students are using standard rulers with numbers on the markings, they believe that the numbers are counting the marks instead of the units or spaces. They just need additional time to explore this concept on their own.
In this lesson we will be focusing on the following Mathematical Practices:
MP.5. Use appropriate tools strategically.
MP.6. Attend to precision.
MP.7. Look for and make use of structure
I ask students to move to their assigned partner. I give them a bucket of measurable objects, paper, and pencil. I model and explain what they will be doing. First I pull an object from the bucket. I measure the object, and write my findings on the board. Then I pull a second object from the bucket. I measure the object, and write my findings on the board.
Car truck: 5 inches
Pencil: 6 inches
How many inches did I measure in all? 6 + 5 = N
I set my timer for about 10 minutes, and ask students to pull two objects out of their bucket. Then, I ask them to measure both objects, and share their findings with their partners. After you both have agreed on the correct measurements, add them together to get the total. As students are working, I circle the room to ask probing questions. I ask the following:
Did any of you come up with a different measurement? Explain
I want to see if they know how to place an object to be measured. Most students begin measuring on zero.
How does the ruler assist you in finding the sum of both objects?
We used the ruler to get an accurate measurement to add.
We used the ruler to count the number of inches in all.
I proceed by asking them to measure two more items, and to determine the total for both items. Students seem to catch on very quickly. I may continue this process a few more times, just to make sure students have time to explore.
In this portion of the lesson, I want to assess my students ability to add unit of measurement using a number line. I want to be sure understand the relationship to the size of a unit and the number of units needed. To do this I ask students to return to their assigned seats. I explain that they need to show their work by explaining how they got their answers. I review student response sheet, so that they can fully understand what they need to do.
As students are working, I circle the room to check for understanding. For instance, I ask students to demonstrate how to measure an object. Can you count the number of units? Are they the same as the number of inches added? If so, Explain?
Students seem to make the connection to the units and number of units counted.