Lesson 10: Counting with Variables

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Discuss: Which of the following types of information change over time?

• Your first name
• Your birthday
• Your height
• Your age
• The temperature outside
• The answer to 2+2
• The capital of our country
• Today’s date
• The score in a game

Do This: Have students discuss which information would change over time and which would not. Some items might generate a larger discussion. For example, it is possible to change your first name or use a nickname. Also, over time, your height will stop changing.

Display: Show “Reflect” slide

Reflect: When is it useful to change what is stored in a variable?

Discussion goal: Students should understand that they can create a variable that stores information that either stays the same or changes over time. In a game with points, a variable is responsible for keeping track of a user’s score throughout the game. Typically, this variable starts out being set to 0 and increases by 1 for every point that the user scores. The final score is reported at the end by printing out the variable.

The goal of this discussion activity is to get students thinking about storing and modifying information using a variable. Students may recall that in previous lessons they would store information, like a word, by entering it into a prompt. In the next activities, students will learn a new way to store information as well as how to modify that information as a program runs. They should discuss when it would be necessary to change or update a variable over time.

For the discussion, decide beforehand what strategy will work best for your classroom. Some ideas include: using a T-chart, discussing in pairs or as a class.

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The value stored in a variable can change over time.

When we start, our count variable is set to 0. After a few seconds, it increases by 1.

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Do this: Use the lesson slides to review the vocabulary for this lesson. Be sure that students can recall from the lesson where they saw each of these concepts.

When a user enters information into a prompt, the computer stores it with a variable. The prompt can also trigger an event. If the code uses a variable, the computer will look for a matching label to find the stored information.

Students shouldn’t be expected to know how variables will be used in this new context right away, so it’s okay to frame these questions as things to consider while they work.

As students move through the levels in this lesson, they will learn how to set a variable to store a number, then change that number over time. Knowing how to modify a variable’s value is the key to tracking something that changes, like the score in a game.

Prediction (3 minutes)

Display: Show “Level 1 - Predict” slide

Do this: Have students read the provided code and make a prediction about what will happen. After pressing “Run”, provide time for students to reflect on anything they found interesting or that surprised them.

Display: Show “Level 2 - Predict” slide

Do this: Have students read the provided code and make a prediction about what will happen. After pressing “Run”, provide time for students to reflect on anything they found interesting or that surprised them.

This lesson includes two prediction puzzles: one to bridge what students have already learned and a second one to introduce the new blocks in the lesson.

Skill Building and Exploration (10 mins)

Display: Show “Level 3-5 - Skill Building” slide

Transition: Move students to their computers. Encourage students to follow the instructions for each level.

Display: Show “Level 6 - Exploration” slide

Mini-Project (17 mins)

Display: Show “Level 7-11 - Clicker Game” slide

Display: Show “Reflect” slide

Reflect: How did you use variables in your game?

Discussion goal: Students should understand that the variables in their game stored a value that changed over time. A variable’s value can set directly in the code, modified as a user interacts with an app, or input directly such as with a prompt.