That's the Mystery Boxes activity. 0. Introduction I 1. The Mystery Box activity shows something more, though. You can build something pretty complex even if all you have figured out are how to use simple building blocks. There are many ways to answer the question of how technology works.
Some patterns are specific to a single technology.
This pattern of building complex systems from simple components is especially applicable to all digital electronics, which includes computers and the ubiquitous microprocessor. Computer programming can be instructive of how computers work, but this can take longer than one or two class periods and is not as general. The lesson was designed to bring a widely-applicable pattern of how technology works to a young audience that may pursue areas of technology not yet invented. In your lifetime, systems of technology have grown very large and complicated. Sometimes the individual pieces are familiar and easy to understand.