Constant of Proportionality Lesson Plan

Constant of Proportionality Lesson Plan


Ever wonder why your cell phone charger gets so hot? Or how different devices plugged into the same charger take different amounts of time to charge?

Believe it or not, it has a lot to do with the constant of proportionality!

Use this artistic, real-life lesson plan to teach your students about the constant of proportionality and how to find k from graphs, equations, and tables. Students will learn material with artistic guided notes, practice and check for understanding with doodle math and mazes, and wrap up with the real life application of constant of proportionality for cell phone chargers.

Get the Lesson Materials

Constant of Proportionality Lesson — Guided Notes, Color by Number, Applications

Constant of Proportionality Lesson — Guided Notes, Color by Number, Applications


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Learning Objectives

After this lesson, students will be able to:

  • Identify proportional relationships in tables, graphs, and equations.

  • Determine the constant of proportionality (k) for a given proportional relationship.

  • Apply the concept of constant of proportionality to real-life scenarios, such as cell phone chargers and other electronic devices that require charging.


Before this lesson, students should be familiar with:

  • Ratios and proportions

  • Graphing on a coordinate plane

  • Equivalent ratios and their relationship to proportional relationships


1 hour


Key Vocabulary

  • Proportional relationship

  • Constant of proportionality

  • Unit rate

  • Equivalent ratios

  • Coordinate plane

  • Graph

Curriculum Standards

CCSS 7.RP.A.2.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.

CCSS 7.RP.A.2.b

Identify the constant of proportionality (unit rate) in tables, graphs, equations, diagrams, and verbal descriptions of proportional relationships.





  • As a hook, ask students why your cell phone charger gets so hot, or how different devices plugged into the same charger take different amounts of time to charge. Refer to the last page of the guided notes as well as the FAQs below for ideas.

  • Use the guided notes to introduce the concept of proportional relationships and the constant of proportionality. Refer to the FAQ below for a walk through on this, as well as ideas on how to respond to common student questions.

  • Walk through how to determine whether something is a proportional relationship and what the constant of proportionality is in tables, graphs, and equations.

Check for Understanding

  • Have students work through the problems on the check for understanding page, either collaboratively or independently.

  • Walk around and spot-check student answers on the check for understanding activity.

  • Based on student responses, reteach concepts that students need extra help with. If your class has a wide range of proficiency levels, you can pull out students for reteaching, and have more advanced students begin work on the practice exercises.


  • Have students practice finding the constant of proportionality using the Doodle Math activity. Walk around to answer student questions.

  • Fast finishers can dive into the maze activity for extra practice. You can assign it as homework for the remainder of the class.

Real-Life Application

  • Bring the class back together, and introduce the concept of how the constant of proportionality impacts how hot their cell phone charger gets and how fast it charges. Refer to the FAQ for more ideas on how to teach it, including a video!


Additional self-checking digital practice

If you’re looking for digital practice for constant of proportionality, try my Pixel Art activities in Google Sheets. Every answer is automatically checked, and correct answers unlock parts of a mystery picture. It’s incredibly fun, and a powerful tool for differentiation. There’s fall, winter, and spring versions perfect for additional practice.

Additional print practice

A fun, no-prep way to practice constant of proportionality is Doodle Math — it's a fresh take on color by number or color by code. It includes 3 levels of practice, and there’s fall and winter themed versions, perfect for a review day or sub plan around the holidays.


Want to try before you buy?

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