Lesson plan

1. Scale drawings can be the same size, larger, or smaller than the original (C)

teaches Common Core State Standards CCSS.Math.Content.7.G.A.1 http://corestandards.org/Math/Content/7/G/A/1
teaches Common Core State Standards CCSS.Math.Practice.MP4 http://corestandards.org/Math/Practice/MP4
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Lesson objective: Understand that scale drawings may be larger, smaller or the same size as an original figure.

Students bring prior knowledge of proportions from Grade 7, Unit 1; 7.G.A.4. This prior knowledge is extended to scaling dimensions of rectangles as students multiply by various scale factors. A conceptual challenge students may encounter is that dimensions must be scaled using multiplication, not addition. 

The concept is developed through work with photographs, which helps students recognize that each dimensions has to scale up or down by the same factor to keep from distorting the image. 

This work helps students deepen their understanding of numbers because the value of the scale factor relative to 1 determines whether the scale drawing is larger, smaller, or the same size as the original.

Students engage in Mathematical Practice 4 (Model with mathematics) as they scale factors to model the changes made to a rectangular photograph.

Key vocabulary:

  • original figure
  • proportions
  • scale drawing
  • scale factor

Special materials needed:

  • Optional: have students bring in school photos to enlarge or shrink.