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Secret Codes & Ciphers

Sixth graders crack and create secret codes with a Caesar cipher — shifting each letter by a fixed amount to hide a message. Shift “CAT” by 3 and it becomes “FDW.” They encode step by step, then make (and break) their own cipher.

Grade 6Secret Codes & Ciphers50 minutes1 class periodCSTA / ISTEExplicit teaching4 StandardsCSTA
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Lesson at a Glance

Everything you need before the bell rings

Learning Objectives

Students will be able to…

  • ✓Explain a cipher.
  • ✓Encode with a Caesar shift.
  • ✓Decode a secret message.
  • ✓Create your own code.
Essential Question

How can you hide a message so only the right person can read it?

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Lesson Phases
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Vocabulary Terms
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Standards Aligned
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Interactive Task
Put in Order · Interactive

Encode CAT with a Caesar Cipher

Project this and have students put the encoding steps in order (shift each letter by +3).

🔐 Put the encoding steps in order — shift CAT by +3!Try it
Tap “Pick a shift number: +3” first!
The Lesson · Use → Modify → Create (a coding progression with Unplugged practice)

50 minutes, five moves

Tap any phase to open the teacher moves and student actions.

1

Hook — Keep It Secret

6 min

How did people send secret messages before computers?

👩‍🏫 Teacher Moves

  • Show a scrambled word.
  • Ask how to hide a message.
  • Set the goal.

🎒 Student Actions

  • Look.
  • Guess.
  • Get ready.
2

Use — Ciphers

12 min

Students encode.

👩‍🏫 Teacher Moves

  • Send students to Encode CAT.
  • Order the shift steps.
  • Note each letter moves +3.

🎒 Student Actions

  • Order.
  • Say.
  • Note it.
3

Modify — Change the Key

13 min

Students modify.

👩‍🏫 Teacher Moves

  • Try a different shift (+5).
  • Re-encode the word.
  • See the code change.

🎒 Student Actions

  • Shift.
  • Encode.
  • See it.
4

Create — Make & Break

13 min

Students create.

👩‍🏫 Teacher Moves

  • Write a short word.
  • Encode it with your shift.
  • Swap & decode a partner’s.

🎒 Student Actions

  • Write.
  • Encode.
  • Decode.
5

Reflect — Reflect

6 min

Students close.

👩‍🏫 Teacher Moves

  • Say what a cipher does.
  • Say why a key matters.
  • Complete the exit ticket.

🎒 Student Actions

  • Say it.
  • Say.
  • Complete the exit ticket.
Standards Alignment

Built to the standards you report on

Aligned to the CSTA K-12 Computer Science Standards and the ISTE Standards for Students.

CSTA
2-NI-06

Apply methods of encryption to secure data.

CSTA
2-NI-05

Explain how physical & digital security protect data.

CSTA
2-AP-13

Decompose a problem into steps.

ISTE
5 Computational Thinker

Use an algorithm to transform data.

Differentiation

One lesson, every learner

Multilingual Learners

ELL / EMERGING READERS
  • Use a letter wheel.
  • Encode one letter together.
  • Frame: “shift by ___.”

Support & Access

IEP / 504
  • Use a +1 shift.
  • Encode a 2-letter word.
  • Use an alphabet strip.

Stretch & Extend

GIFTED / EARLY FINISHERS
  • Decode a message with no key given.
  • Try a keyword cipher.
  • Explain why longer keys are safer.
Materials

What to gather

  • 📽️Screen / board
  • 🔀Cipher wheels
  • 💻Encode CAT
  • 🔤Alphabet strips
  • 📓Notebooks
  • 🎫Exit-ticket slips
Vocabulary

Key terms — hover for a quick definition

ciphera method to hide a messageencodeto turn a message into a secret codedecodeto turn a code back into the messageCaesar ciphershift each letter by a fixed amountshifthow many letters to move each onekeythe secret needed to decode (the shift)encryptionmaking data unreadable without a keydecryptionmaking encrypted data readable again
Evaluate

Exit Ticket

Preview the three formative checks. Tap “Sample answer” to see what mastery looks like — hide them before you print for students.

QUESTION 1
What does a cipher do?
Hides a message so only the right person can read it.
QUESTION 2
Encode “CAT” with a +3 Caesar shift.
FDW.
QUESTION 3
What is the “key” in a Caesar cipher?
The shift number you need to decode.

Reflect: secret codes & ciphers.

Have students encode their first name with a +3 Caesar shift. A printable cipher worksheet is in the Computer Science library.

Study · Flashcards

Study the key terms

Tap a card to flip it, then rate whether you knew it. Built from this lesson’s vocabulary.

🃏 CS Secret Codes and Ciphers (Grade 6)Flip
Card 1
Term
Tap to flip →
Meaning
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Practice · Quiz

Check your understanding

A quick self-check with instant feedback, drawn from this lesson’s key terms.

📝 CS Secret Codes and Ciphers (Grade 6)Quiz
Score: 0
1 / 6
Question 1
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Practice · Worksheet

Printable worksheet

A print-and-go review sheet with a built-in answer key. Tap “Show answer key” to reveal answers, or print the clean version for students.

🖨️ CS Secret Codes and Ciphers (Grade 6)Print
Name: ________________________
Date: ____________

Part A · Write the word that matches each meaning

Word bank: Caesar cipher, cipher, decode, decryption, encode, encryption, key, shift
  1. how many letters to move each one
  2. to turn a message into a secret code
  3. making data unreadable without a key
  4. the secret needed to decode (the shift)
  5. to turn a code back into the message
  6. a method to hide a message
  7. shift each letter by a fixed amount
  8. making encrypted data readable again

Part B · Show what you learned

  1. What does a cipher do?
  2. Encode “CAT” with a +3 Caesar shift.
  3. What is the “key” in a Caesar cipher?
Answer key — Part A: 1) shift · 2) encode · 3) encryption · 4) key · 5) decode · 6) cipher · 7) Caesar cipher · 8) decryption
Part B: 1) Hides a message so only the right person can read it. 2) FDW. 3) The shift number you need to decode.