This is the latest material I have made for my Codes and Ciphers club. It involves showing both the ciphertext and the plaintext for messages using each of five ciphers alongside another ciphertext that uses the same cipher (the process and the key are identical).
1.2.1/this is a secret message
2.2.1/we do not care for those people and their reckless sense of unchecked optimism
3.2.1/every time we deal with an enemy we create two more
4.2.1/she sells sea shells by the sea shore
5.2.1/they say mexico will pay for it
Using the first cipher, "nothing beats waffles" becomes "sftgtonaaehnibsewfl".
Each "key" in the second cipher is meaningful, but not every part of each key is meaningful.