We've been using pair and group work in language classes for a long time, but those are all remarks I still hear from teachers. Such views are worrying because almost all classroom materials include exercises where students are expected to work together in pairs or in groups. It just seems that some students still prefer their teacher to lead them and guide them and correct them -- or is it that they don't want to talk to each other? Anyhow, pair and group work doesn't seem to be everyone's cup of tea.
Under such pressure from students, it may be tempting to reduce the emphasis on pair and group work -- but, if anything, I think there should be more emphasis. This is because pair and group work does seem to be the most effective way (the only way?) to involve students in natural communication in English in the classroom -- especially when the classroom is probably the only place they do speak English. In fact, the larger the class, the greater the need to work in pairs and groups -- otherwise hardly anyone gets a chance to speak English in class.
For example, rather than have students working as individuals, I'd choose to do pair or group work in these situations:
When students are doing a blank-filling exercise or a multiple-choice quiz. Discussing the possible answers and trying to reach agreement is a really good way of using English to communicate ideas. The exchange of views between students, as they collaborate to get the answers right can easily lead to natural communication in English. In some ways, an exercise is quite similar to a problem-solving task: the students work together to "solve" the exercise -- possibly in competition with other pairs. This can be fun too! (This works for reading comprehension exercises too.)
After doing a listening exercise. Instead of simply going through the correct answers, allow time for the students to work in pairs comparing their answers. If there are any questions they couldn't answer, or any discrepancies between their answers, there's a strong motivation to want to listen to the recording again and find out who was right. This kind of discussion is an ideal opportunity for students to communicate with each other.
After students have written a composition for homework, put them into small groups and ask them to read each other's work and comment on it. Any piece of writing should be an attempt to communicate ideas to a reader. If students know that their peers are going to read their work, they're more likely to try to make it interesting, informative and entertaining! If you, their teacher and 'critic', are the only reader, the process of writing is much less motivating.
Discuss topics in small groups, not as a whole class. This gives more students a chance to give their opinions, rather than saying or thinking "I agree with what she just said." Many students feel shy about talking in front of the whole class, and feel more relaxed and confident in a small group -- and everyone can have their say without pressures of time or embarrassment.
While doing problem solving and discussion activities students are participating in enjoyable speaking activities. But their enjoyment (or frustration at not being able to express themselves easily in English) may tempt them to lapse into Japanese from time to time (or more frequently). When this happens, you might find it helpful to remind them that every member of the class has a common aim: to improve their English. Agree together on this rule: "Only English may be spoken in our class." That may sound like a tall order, but it's something everyone should aim for. (It's OK, of course, for students to ask each other "How do you say so-and-so in English?" or "What's the English word for so-and-so?")
Here are some more ideas that may help if your students are finding it really difficult to stick to English all the time:
To sum up: If students want to develop their fluency and confidence, so that in real life they can communicate in English, then the only way they can do it is by communicating with each other in English -- in pairs and in groups.
Another reason why students may be talking in Japanese is that the activity is too difficult or too confusing for them. Open-ended activities are quite challenging. Students won't possess all the language they require to participate easily and fluently. There are several ways of getting around this problem, not all of which will be necessary at the same time:
Make sure that any pair or group work is integrated (before, during, and after) with other activities. Feedback is important. After any pair or group work activity, reassemble the class and give them feedback: mistakes you've noted down, advice on expressions or vocabulary to use -- and praise. And, questions from them.