This memo reports the results of a case study into how children learn in the absence of explicit teaching. The three subjects, an eight year old, a ten year old and a thirteen year old were observed in both of two experimental micro-worlds. The first of these micro-worlds, called the Chemicals World, included a large table, a collection of laboratory and household chemicals, and apparatus for conducting experiments with chemicals; the second, called the Mork and Mindy World included a collection of video taped episodes of the television series Mork and Mindy, a video-tape machine and experimenter with whom the subjects could discuss the episodes. The main result of the study is a theory of how children's interests interact with knowledge embodied in their environment causing them to learn new powerful ideas. An early version of this theory is presented in chapter five.