A classroom activity that I think would be a useful way to help students understand encoding and decoding would be the decoding and creation of ciphers. I, as the teacher, would create a cipher with multiple different messages that I would have my students decode in groups. once they have finished that I would get them to create their own cipher, write 2-3 messages and have other groups attempt to decode it. I think it is a great activity for learning the practicality of encoding and decoding, and it allows for student collaboration. At the end of the lesson I would have a class discussion about how everyone went, if it was difficult, easy or mild, how they found it and if they would do anything differently next time.