General Information
Subject Area: Mathematics (B.E.S.T.)
Grade: 2
Strand: Geometric Reasoning
Date Adopted or Revised: 08/20
Status: State Board Approved
Benchmark Instructional Guide
Connecting Benchmarks/Horizontal Alignment
Terms from the K-12 Glossary
- Pentagon
- Polygon
- Rectangle
- Square
- Triangle
Vertical Alignment
Previous Benchmarks
- Perimeter is a new concept in grade 2.
Next Benchmarks
Purpose and Instructional Strategies
The purpose of this benchmark is for students to use the attribute of side length to find the perimeter in the context of familiar two-dimensional figures.- Instruction includes the use of properties of addition to help students think and solve flexibly.
- Instruction includes the use of a number of sides as a defining attribute of triangles, rectangles, squares and pentagons to help them solve problems.
- Instruction includes recognizing that when given a rectangle the opposite side lengths are the same
- Instruction includes using linear tools such as toothpicks, straws, popsicle sticks, etc. to explore perimeter as additive.
- For example, students can be given dimensions of a figure and asked to build the figure’s boundary using toothpicks or straws. Students can then write an addition expression or equation to represent the perimeter.
- Instruction includes applying the commutative and associative properties to find the perimeter of a figure.
Common Misconceptions or Errors
- Students may misalign the ruler with the object and measure an object from 1 instead of 0.
- Students may count all tick marks, not just the whole-unit marks, when reading a ruler.
- Students may leave gaps when measuring objects.
- Students may need support in making the connection to the commutative and associative properties when determining the perimeter of a figure.
Strategies to Support Tiered Instruction
- Teacher models how to measure starting at the zero point on a ruler or meter stick demonstrating how measuring an object starting at one instead of zero will give an incorrect measurement. Students can then demonstrate how to measure other objects using a meter stick.
- Teacher has students write ‘0’ at the appropriate location on a ruler and provides instruction on using a ruler to measure length.
- Instruction provides opportunities to measure lengths of segments and objects to the nearest whole number using a ruler scaled in centimeters and inches. Teacher provides feedback as needed.
- Instruction includes opportunities to compare a regular ruler to a ruler that only has tick marks for the whole numbers on it. Teacher demonstrates how to measure using the modified ruler and then the regular ruler on the same object. Students compare the two rulers.
- For example, teacher prepares a whole unit ruler by using a regular ruler to make a line that is 12 inches long and marking only the whole number units along the way (same for centimeters).
- Teacher provides color tiles to transition to measuring with rulers. Students measure the lengths of a line segment using one-inch color tiles, first with gaps and record the answer. Then, they measure with tiles again without the gaps and record the answer. The teacher discusses why they are different measurements when the line didn’t change? Finally, the students measure the lengths of the line segment again using a ruler and discuss which tile measurement was correct and why.
- Teacher uses straws cut to varying lengths of 1, 2, 3, 4 or 5 inches. Given side lengths, students build a figure. Then, decompose the figure by laying the straws end-to-end against a ruler. Rearrange the straws against the ruler to show that the perimeter will remain the same regardless of the order in which the straws, or values, are added.
Instructional Tasks
Instructional Task 1 (MTR.3.1)
Provide pre-cut straws of varying lengths.- Part A. Construct polygons according to their defining attributes.
- Part B. Use a ruler to measure and determine the perimeter of the each figure.
Instructional Items
Instructional Item 1
Bill wanted to plant a small garden with the measurements shown below. He wants to buy a fence to go around the perimeter of the garden. How much fence should Bill buy?
*The strategies, tasks and items included in the B1G-M are examples and should not be considered comprehensive.