Second grade students transition from measuring lengths with informal or non-standard units to measuring with standard units—inches, feet, centimeters, and meters—and using standard measurement tools.
Students learn the measure of length as a count of how many units are needed to match the length of the object or distance being measured. Using both customary (i.e. imperial) units (inches and feet) and metric units (centimeters and meters), students measure the length of objects with rulers, yardsticks, meter sticks, and tape measures. Students become familiar with standard units (e.g., 12 inches in a foot, 3 feet in a yard, and 100 centimeters in a meter) and how to estimate lengths. In grade two, students also connect the concept of the ruler to the concept of the number line. These understandings are essential to supporting work with number line diagrams.
This is an example of using a number line drawing to solve a word problem.
There were 27 students on the bus. Nineteen (19) students got off the bus. How many students are still on the bus?
Student: I used a number line. I saw that 19 is really close to 20. Since 20 is a lot easier to work with, I took a jump of 20. But, that was one too many. So, I took a jump of 1 to make up for the extra. I landed on 8. So, there are 8 students still on the bus. What I did was 27 – 20 = 7, and then 7 + 1 = 8.