On the continuum along which theories of first and second language acquisition are located, the two extremes represent the classic controversy of nature (nativist) vs. nurture (environmentalist), while those in the middle view language acquisition as a result of a more or less balanced interaction between innate capacities and linguistic experience (interactionist). Interactionists can be divided into two groups according to whether they give more weight to cognitive or social factors. As a rule, cognitive interactionists give more weight to the learner and thus reflect to a greater extent the influence of nativist theories, while social interactionists focus on language in communication and so are closer to the environmentalist part of the continuum. An examination of these approaches provides a framework for evaluating some of the major research findings in second language acquisition as they relate to classroom foreign language teaching. Based on research findings, it is now recognized that certain properties of second and foreign language acquisition are immune to environmental differences. Nonetheless, the environment plays an essential role in determining how much and how quickly learners learn. Therefore, language learning must be viewed as the outcome of the interaction of experience with the cognitive, linguistic, and social systems. (42 references) (MSE)