ABSTRACT Much of the recent research in second language acquisition has focused on the learner rather than on the teacher and has been undertaken not in foreign language teaching but rather in bilingual education context, in which second language acquisition takes place through functional use rather than through formal instruction. However, research findings suggest that primary school children exposed to bilingual immersion-type programs which lack a second language speaking peer group tend to develop pidginized version of the second language. Therefore, formal foreign language teaching may be needed even in bilingual immersion programs for primary school children. Even in exposure to a peer group, second language teaching can make at least a short run difference in improving grammatical use and correctness. Data from a study recently undertaken at Stanford University show that certain types of language teaching behaviors (e.g., modeling, using visual aids, etc.) relate significantly to pupil achievement as measured by comprehension and production tests. A plea is made for (1) foreign language teaching research undertaken by foreign language specialists using behavioral categories related directly to the foreign language curriculum, (2) a combination of functional and formal approaches (e.g., bilingual education and second language teaching) to achieve second or foreign language proficiency.