When a particular language feature is introduced for the first time, or when the teacher feels there is a need for correction of a persistent problem, it is appropriate to use narrow-focus materials that isolate one element in a context where other things seem easy. But it would be a disservice to students to use such materials exclusively or even predominantly. We should remember that learners who successfully acquire a second language outside classrooms certainly are exposed to a great variety of forms and structures they have not mastered.