Lesson plan

2. Understand that area is measured in square units (C)

teaches Common Core State Standards CCSS.Math.Content.3.MD.C.5 http://corestandards.org/Math/Content/3/MD/C/5
teaches Common Core State Standards CCSS.Math.Content.3.MD.C.5a http://corestandards.org/Math/Content/3/MD/C/5/a
teaches Common Core State Standards CCSS.Math.Content.3.MD.C.5b http://corestandards.org/Math/Content/3/MD/C/5/b
teaches Common Core State Standards CCSS.Math.Practice.MP2 http://corestandards.org/Math/Practice/MP2

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Lesson objective: Understand that square units or unit squares (that cover a figure without gaps) can be used to measure the area of a figure, which is said to be n square units.

Students bring prior knowledge of partitioning rectangles into equal squares from 2.G.A.2. This prior knowledge is extended to developing the understanding that counting square units is a way to measure area, as students find the area of rectangular grass lawns by partitioning them into equal square units and then skip counting or using repeated addition to find the total number of square units that cover the rectangle. A conceptual challenge students may encounter is confusing measuring area and measuring length. Students may think that a longer rectangle has a greater area.

The concept is developed through work with rectangles partitioned into equal-sized squares, which can be counted to express the area of the rectangle. These squares are identified as square units.

This work helps students deepen their understanding of number because they are using the number of square units to measure and compare the size of the rectangles.

Students engage in Mathematical Practice 2 (reason abstractly and quantitatively) as they use drawings to represent the two lawns and think about their relative size by partitioning the drawings and counting squares. This will lead to an understanding of the concept of square units as a square with side lengths one unit.

Key vocabulary:

• area
• length
• partition
• square meter
• square unit
• unit square
• width