The sheet is a story about a spy.
Students should use the tally sheet to undertake a frequency analysis of the sheet.
This quickly (they don't need to do the whole thing) reveals the letters T and E, and by dedcuation (eg common occurance of T*E gives away H), the students can read the whole sheet. They really enjoy this... much nicer way of practicing tally.
Can make excellent links to Queen Mary and Babbington, where frequency analysis was used to secure evidence that Mary was a traitor and eventually led to her excecution. Good to link with Humanities department.
These stories are really easy to make - write one on word then choose a symbolic font. can make stories about your school etc.