At its most basic this task is an exercise in reading and recording information from a table. It also offers opportunities for children to do some elementary reasoning as they compare results with each other and work out why they differ.
Write the two names, Jim and Jan, on the board and ask the children what is the same and what is different about them. (If you have large letter tiles you could use these to construct the names instead.)
Talk about codes and how sometimes letters are turned into numbers to make a message more difficult to understand. Copy the table onto the board ( or show this PowerPoint slide) and ask the children if they can work out what the letters in Jim's name are worth. Record them and confirm that the children realise there is a many to one correspondence, letter to number.
Explore a couple of longer names, then offer the children some time to explore their own names and those of their friends.
Bring the children back together again and write 1 4 7 , 1 5 5 5 and 1 5 4 8 on the board, together with the names Andy, Anne and Amy. Could they work in partners to work out which name is which set of letters? Share the children's explanations and then hand out this sheet. Emphasise that you are interested in how they work out which name is which as well as whether they work them out correctly.
How will you record what you are finding out?
How did you know which set of numbers are which name?
What were your clues?
Once children have worked out the codes on the sheet, challenge them to invent a set of names and codes for themselves, and to offer them to others in the class to solve. This will give them an additional insight into what makes a good code.
Others could make up a code using symbols instead of numbers. There is a blank set of letter cards to download which may prove useful.
You can download a set of letter cards which some children may find useful to manipulate.