ALEX Lesson Plan

Cracking the Code

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  This lesson provided by:  
Author:Kathy Perkins
System: Tuscaloosa City
School: Tuscaloosa City Board Of Education
The event this resource created for:ASTA
  General Lesson Information  
Lesson Plan ID: 34771


Cracking the Code


Codes are used to transmit messages.  We may use codes to keep our messages secret from people who do not know the code, or we may use them to change one type of information into another.  The key to decoding a message is knowing the rule to crack the code.  In this lesson, students will explore different types of codes, create coded messages, and apply rules to decode messages. 

This lesson provides the background needed for students to then develop their own method for transferring information.

This lesson results from a collaboration between the Alabama State Department of Education and ASTA.

 Associated Standards and Objectives 
Content Standard(s):
SC2015 (2015)
Grade: 4
7 ) Develop and use models to show multiple solutions in which patterns are used to transfer information (e.g., using a grid of 1s and 0s representing black and white to send information about a picture, using drums to send coded information through sound waves, using Morse code to send a message).*

Alabama Alternate Achievement Standards
AAS Standard:
SCI.AAS.4.7- Identify models that show ways in which patterns are used to transfer information (using drums to send coded information through sound waves, using Morse code to send a message).

Local/National Standards:


Primary Learning Objective(s):

Students will:

  • use multiple codes to transmit and decode messages.
  • explain the uses of different types of codes.

Additional Learning Objective(s):

Students will:

  • discuss the development of codes through history.
  • use binary and Morse codes to send and receive messages.
  • create codes using hand signals and sounds, and use these codes to send and receive messages. 
  • create images and transmit those images to others using codes.
 Preparation Information 

Total Duration:

Greater than 120 Minutes

Materials and Resources:

  • Binary code handout from for each student
  • Optional: Binary code poster (printed on poster maker from binary code handout
  • 1" x 9" strips of construction paper (one per student)
  • tape
  • markers, pencils
  • copies of p.4 and 5 from CS Unplugged packet for each student; print p. 2 for teacher reference
  • copies of "Message Received!" recording sheet for each student (See Attachments section.)
  • one copy of "Pictures for Message Received Game" handout for every 6 students; cut into 6 pieces so each student receives one image (See Attachments section.)

Technology Resources Needed:

  • computer with Internet connection and projector or interactive whiteboard


Background information is embedded in the procedures. The following websites also provide good information about codes:


Engage (15 minutes):

  1. Ask what they already know about codes. Have volunteers explain how codes work (symbols, sounds, or patterns stand for letters or words to create a message that can only be understood by someone who knows the code).  Have students brainstorm a list of codes used in the past and currently.


    • Writing is a form of code that uses written symbols to change spoken language and thoughts into graphic form.
    • Sign language is a code that uses hand signals for letters and words.
    • Drum codes and smoke signals were used by ancient people to communicate across distances.
    • A referee’s hand signals at a football game communicate calls.
    • Semaphore (flag signals) are used to communicate between boats.
    • Telegraph companies and the military used Morse code to communicate before phone communication was possible.

2. Access the Morse Code Translator on the teacher's computer.  Type in a message and click translate to show it in symbolic Morse Code.  Click play to hear the audio translation of the code.  Ask how Morse Code could be used, both when it was first invented in 1836 and today to send SOS signals using lights or electronic pulses when other forms of communication are limited.  

3. Watch 5-minute “History of Morse Code” video on YouTube.  Discuss that while Morse code can be expressed as dashes and dots, it is more commonly an audible code as they heard in the video.

Explore (25 minutes):

  1. Codes like Morse code were first used to transmit messages across large distances.  Now that communication technology has advanced with the advent of cell phones and the Internet, different types of codes are more common.  Introduce the term “binary” and explain that it is the code used by computers to understand letters and numbers.
  2. Show video for the “Binary Bracelets” lesson (1.5 minutes).  Ask students why computers use binary code. (Since robots and computers are composed of thousands of electrical switches that are either “on” or “off,” this code can be used to represent letters and numbers with sequences of only two options.)
  3. Give students binary code handouts, strips of construction paper, markers, and tape.  Using a binary code poster or a projected image of this handout, discuss the 8-symbol code for each letter, which could be thought of as “on” and “off,” “0’s” and “1’s,” “black and white,” or any set of opposites, much the same way as Morse Code is dashes and dots.  Have each student circle his or her first initial on the handout and create a “binary bracelet” by drawing the binary code for that letter on the strip of paper.  Tape on wrists.
  4. Have students continue to use binary code by decoding the secret message at the bottom of the page.  Students’ success with decoding the secret message can be a formative assessment of their understanding of binary code.

Explain (30 – 40 minutes):

  1. Codes can be used to transmit verbal messages, but they can also be used to transmit data such as images.  When you see a picture on a computer or television, that picture is made of thousands of tiny dots called pixels.  The machines transmit these pictures by communicating the color and arrangement of these pixels to make a picture.  (Increase the zoom on your computer to begin to show pixels; talk about how zooming on a low-resolution photo results in a more pixelated image.)
  2. Watch the 2.5-minute video about image compression and transmission of pictures. 
  3. Provide background information to students about image compression (see p.2 of "Unplugged Computer Science: Image Representation").  Project p. 3 from the packet so students can see it and walk students through the compression code for the letter “a.”  Have a student volunteer create a new image on the grid at the bottom of the page, and then have students work in small groups to write the compression code for the image.  After groups have completed the code, have a student from each group fill in a line or two of the code on the board or projected image.  This gives students a chance to self-check their thinking and ask questions before creating and decoding more codes independently.
  4. Distribute image compression handouts (p. 4-5 copied front and back).  Students will decode images from a provided code on p. 4.  Then they will create their own images and write codes for them on p. 5.  Circulate as students work on these tasks to guide understanding as necessary.  

Elaborate (30 minutes):

  1. Tell students that they will create a new code they can use to communicate a message using only sounds they can create without using their voices.  Examples are claps, desk taps, foot stomps, etc.  Have students work in groups of four.  As students work, circulate and ask guiding questions:
    • How can they make the code?
    • How will the message receiver be able to understand it? 
    • Do you need a code for each letter of the alphabet?
    • Will you have a sound that represents a space between words, or should the receiver be able to detect spaces by the rhythm of the code?
    • Are there some letters that are more important or more common than others?  How will this affect your decision for sounds for each letter?  
    • How will you share your key with the whole team?

2. After 20 minutes, split teams into a communication team and a receiver team.  Give the communication team a slip of paper with a simple sentence to transmit.  One team at a time, communicators send the message to their receiving team.  After the code has been transmitted, the receiving team tells the rest of the class what they decoded.  Then the communication team reads the slip of paper aloud to check the decoding from the receiving team.

3. Debrief by discussing problems encountered during code creation, transmission, and decoding.  Common problems will include difficulties coming up with unique codes for each letter of the alphabet, understanding boundaries between letters and words, and the availability of a key for all team members.  Discuss why computers are commonly used today to create, transmit, and decode messages.  

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Assessment Strategies

Play "Message Received" game with a partner.  

  • Each person gets a picture on graph paper. (Cut apart picture cards on the attached handout.)  For the first round, students use a written letter code to transmit the data in the picture without allowing the partner to see the picture.  For example, if the student gets a picture of a rocket, he will write the code for the word rocket in binary or Morse code.  He will pass the code to his partner.  The partner will decode the message and write the word underneath the code and return it to the original partner to check.
  • Each partner will work on a code for a different picture at the same time so everyone is actively engaged.  If the message is incorrect, partners will circle the incorrect letters and check to make sure the code was accurate.
  • Recording sheets can be used to determine whether students demonstrate accuracy in coding and decoding, understanding of the reasons for using different codes to accomplish different tasks, and the ability to transmit the same message in multiple ways.  


Students can continue to explore binary and the idea of computer coding by beginning the “Hour of Code” or "Course 2" on  Students can create individual accounts using their school email addresses or they can work without signing in.

Following exploration of this concept, students can apply what they have learned about transmitting codes and can develop their own system for relaying a message over a distance.


During the "Explain" phase of the lesson, students can experiment with creating graph paper pictures and image compression codes online. (This site originally appears in Japanese, but the page can be translated in the Google Chrome browser.)  The site will translate any image the student creates into compression code, giving the student more support in the code creation process.

View the Special Education resources for instructional guidance in providing modifications and adaptations for students with significant cognitive disabilities who qualify for the Alabama Alternate Assessment.