The instructor makes the decisions about what to do next. The students know whether their responses are correct because the instructor tells them. The students learn information laid along a predetermined path. The students are expected to understand established models and paradigms. The student controls the situation.
Students make their own decisions about how to organize their learning time.
Students know they are wrong when something doesn't work. Students are exploring. Students are expected to develop their own cognitive models. A course should involve some of both types of instruction, as well as some interaction which combines the two. Despite the frequent and justified calls for student-centered instruction, there are times when students do better under the guidance of someone else.