One of the most important concerns of a teacher is to make sure that all of his students are actually working. In this regard, the language lessons are particularly at risk, because oral activities take a greater part in them.
When you do an exercise in written, all the students try to answer the questions simultaneously, obviously some of them with more seriousness than the others, but, still, all of them have to do at least something to avoid troubles when it comes to the correction. And it’s not difficult for the teacher to walk between the ranks and to look after the children. During an oral lesson, the attention of the teacher is usually taken by the lesson itself. It’s less easy to awake the lazy students.