The early chapters of this book trace the attempts to explain classroom language learning in terms of general theory of learning (behaviorism) and the study of naturalistic language learning. The middle chapters document the attempts of researchers to enter the "black box" of the classroom in order to describe the teaching-learning behaviors that take place there and to investigate to what extent and in what ways instruction results in acquisition.

The book concludes with a theory of classroom language learning. This theory advances an explanation of the relationship between explicit and implicit linguistic knowledge and in so doing accounts for how both form-focused and meaning-focused instruction contribute to second language acquisition in the classroom.