Presentation and use of formally-specified software components in CS1/CS2 presents interesting pedagogical challenges. Specifications may involve unfamiliar mathematical concepts and notation. We have found that the use of toys, such as stacking plastic cups and Lego blocks, to be amazingly effective in helping students develop mental models for mathematical concepts. With the aid of these mental models, students are able to understand the behavior of software components through cover stories --- their specifications --- without knowing the implementations of the components. 1. A PEDAGOGICAL CHALLENGE System thinking offers a worldview that underlies all component-based engineering, including software engineering. By system thinking, we mean viewing or understanding things as units that can be viewed from the outside --- the client view --- as indivisible, or from the inside --- the implementer view --- as compositions of other systems, a.k.a. subsystems [4]. Our CS1/CS2 sequence ...

As I write this sentence, I am glancing over at the color printer sitting beside my screen. In the popular jargon of the computer industry, that printer is called a "peripheral"—which, upon reflection, is a rather odd way to describe it. What, precisely, is it peripheral to? If the ultimate