ALEX Lesson Plan


To Scale or not to Scale?  That is the Factor.

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  This lesson provided by:  
Author:Caleb Salamone
System: Blount County
School: Cleveland High School
  General Lesson Information  
Lesson Plan ID: 32244


To Scale or not to Scale?  That is the Factor.


Students will learn to solve proportions and find missing sides of similar figures using the scale factor.  This lesson is best taught before the concept of cross multiplication is developed.  Not only will the student learn the process of using a scale factor to find a missing value from a proportion, but they will also practice these skills in a timed game online.  They will realize that the scale factor is sometimes not an integer, and some proportions are more difficult to solve.  This lesson is a great precursor to the means and extremes property of proportions also known as cross multiplication.

 Associated Standards and Objectives 
Content Standard(s):
MA2015 (7)
2. Recognize and represent proportional relationships between quantities. [7-RP2]
a. Decide whether two quantities are in a proportional relationship, e.g., by testing for equivalent ratios in a table or graphing on a coordinate plane and observing whether the graph is a straight line through the origin. [7-RP2a]
b. Identify the constant of proportionality (unit rate) in tables, graphs, equations, diagrams, and verbal descriptions of proportional relationships. [7-RP2b]
c. Represent proportional relationships by equations. [7-RP2c]
Example: If total cost t is proportional to the number n of items purchased at a constant price p, the relationship between the total cost and the number of items can be expressed as t = pn.
d. Explain what a point (x, y) on the graph of a proportional relationship means in terms of the situation, with special attention to the points (0, 0) and (1, r) where r is the unit rate. [7-RP2d]
MA2015 (7)
3. Use proportional relationships to solve multistep ratio and percent problems. [7-RP3]
Examples: Sample problems may involve simple interest, tax, markups and markdowns, gratuities and commissions, fees, percent increase and decrease, and percent error.

Local/National Standards:


Primary Learning Objective(s):

The student will learn that similar figures have sides that are proportional.  They will also learn to find a missing part of two similar figures using the scale factor.  Using this information, they will evaluate real life uses of this concept.  Students will also learn how to find missing values in a proportion quickly and efficiently.

Additional Learning Objective(s):

 Preparation Information 

Total Duration:

31 to 60 Minutes

Materials and Resources:

Mini Whiteboards and markers are optional

Technology Resources Needed:

Students need a computer or web tool to access video1 and video 2 (attached below) and an online game.

The teacher needs a computer, digital projector, and audio equipment to display the video for students to be introduced to the lesson.


Students should already have a good understanding of rates and ratios.  Students may have already experimented with proportions, but they have definitely been in the process of defining similarity as corresponding angles are the same, and they have the same shape.


-The first video would be a great launch for this lesson.

-Today we are going to talk about a way to organize the relationships between corresponding sides of similar figures. This will be done using proportions which are two equal ratios.

-The second video attached below is full of content on how to not only set up and label a proportion, but it also emphasizes the use of a scale factor.

-Once both videos have been viewed, have students practice on a few basic proportions provided to them via slideshow presentation (attached).  They can use their whiteboards to display the answer to each part of the slideshow practice problems.

-Have them practice using scale factors to determine the missing value until they are comfortable.

-Introduce them to the dirt bike proportion game and play a round with them coaching you along. I suggest you miss a few to show them that accuracy is important or the dirt bike slows down instead of speeding up.

-Show them how to sign up and find people to play against. I recommend that you experiment with the game so you are familiar with how to set up a private game with a password. (Keep your school's Acceptable Use Policy in mind)

-Students who use your private game should be able to race against you and their peers.

-Make sure that everyone takes a turn with the game before you assess with an exit pass or group question. Both the practice problems and the exit pass are available on the attached presentation.

-The student will learn that similar figures have sides that are proportional. They will also learn to find a missing part of two similar figures using the scale factor. Using this information, they will evaluate real life uses of this concept. Students will also learn how to find missing values in a proportion quickly and efficiently

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Assessment Strategies

Students will be able to compete in the game with a decent level of sucess.  They should also be able to reason out what the solution to the proportion is, but the speed will vary depending on a students ability.


Have students not only compete with other students, but have the fastest students compete against each other.  They also should use this information to solve real life application problems like those found here.


Students who need extra help could benefit from practice scaling a fraction up or down using whole numbers and then move into what multiplying by 1.5 and 2.5 does to a number.  Here is a site that uses this method.

Each area below is a direct link to general teaching strategies/classroom accommodations for students with identified learning and/or behavior problems such as: reading or math performance below grade level; test or classroom assignments/quizzes at a failing level; failure to complete assignments independently; difficulty with short-term memory, abstract concepts, staying on task, or following directions; poor peer interaction or temper tantrums, and other learning or behavior problems.

Presentation of Material Environment
Time Demands Materials
Attention Using Groups and Peers
Assisting the Reluctant Starter Dealing with Inappropriate Behavior
Be sure to check the student's IEP for specific accommodations.