Prepared on behalf of CaesarCipher.org | Free classroom resource 1 / 2 CIPHER LAB / STUDENT SHEET Predict. Transform. Explain. A short classroom activity for Caesar shifts, wraparound and reversible rules. Work on paper first, then check a harmless example with a tool. Name: __________________________ Date: __________________ 01 / Agree on the rules Use the English alphabet A-Z. A forward Caesar key of 3 maps A to D. Copy spaces and punctuation unchanged for this worksheet. Keep your prediction separate from the checked result. Input Forward key Your prediction CAT 3 ________________ XYZ 3 ________________ DOG 5 ________________ 02 / Reverse one transformation KHOOR was made with a forward Caesar key of 3. Decode it, then encode your proposed answer again to check it. Proposed plaintext: __________________ Re-encoded result: __________________ 03 / Compare two rules With the standard A-Z alphabet, Atbash maps A to Z, while ROT13 maps A to N. Both undo themselves when applied twice, but they are different transformations. Apply Atbash to CAT: __________________ 04 / Explain what the test shows Why does a shift of 29 behave like a shift of 3? ________________________________________________________________________ Does a readable candidate prove it was the intended message? What context would help? ________________________________________________________________________ Check only after predicting: Caesar tool | Atbash tool Prepared on behalf of CaesarCipher.org | Free classroom resource 2 / 2 CIPHER LAB / FACILITATOR NOTES Check the rule, then discuss the evidence. Answer key and a compact plan for a 15-20 minute learning activity. Prepared on behalf of CaesarCipher.org. Answer key Task Result Reason CAT, key 3 FDW Each letter moves forward three positions. XYZ, key 3 ABC All three letters wrap around the alphabet. DOG, key 5 ITL D to I, O to T and G to L. Decode KHOOR, key 3 HELLO Reverse the original forward shift. Atbash of CAT XZG C pairs with X, A with Z, T with G. A short facilitation plan Start (3 minutes): Demonstrate A to D and X to A. Ask learners to state the alphabet and direction in their own words. Predict (5 minutes): Let learners complete the table without a tool. Ask them to explain one wraparound case to a partner. Check (5 minutes): Use the linked tools to compare predictions. Record a corrected answer and the rule that explains the difference. Reflect (3 minutes): A full trip of 26 positions changes nothing, so 29 equals 26 plus 3. A reverse check shows consistency; context is still needed when selecting an intended plaintext from ambiguous candidates. Learning resources CaesarCipher.org - classical cipher tool collection Caesar decoder - inspect candidate shifts Learning guides - rules and worked examples Use harmless examples Historical ciphers are for education and puzzles rather than modern confidentiality. Do not put private messages, passwords or personal information into public class records.