In the old days, computers were humans, often women, who were employed to compute compute compute. Creating a computing app is a great application of the use of variables. Here's a sample of an "area of a rectangle" computer for your reference. (Don't show it to kids. It's just for your reference.) This type of project works well as a beginning project with variables. Once the whole class gains experience with this challenge, you can set the kids loose with an open ended, 'create some other type of computer' challenge.
