This is a study of the processes involved in second language learning in which the principal subject was an Iranian child who learned English in the United States without formal instruction. Some of the questions dealt with in this study include: what motivates language learning in a child; what makes the linguistic structure of a language more or less difficult to acquire; what effect teaching structure has on rule formation; what some of the criteria are for language selection in a multilingual environment; what some of the characteristics are of language switching; what an analysis of discourse can tell us about the process of rule formation in the speech of one second language learner; and whether transformational grammar is an adequate model for describing question development in the speech of one second language learner. The main conclusion is that any theory of language acquisition must consider the many variables that interact in communication. (Author/AM)