[livinginkorea]

To answer the OP (instead of my last ramblings) I think that an English class should be mostly conducted in English, except for some explainations or discipling young leaners. There are loads of tools and web resources out there to help any teacher to get a comfortable knowledge of classroom English and they shouldn't be afraid to make mistakes.

I had one co-teacher before who has great English but was so afraid to make mistakes that they talked only in Korean! Being confident is very important for teachers especially if it isn't there language. We shouldn't correct them too much as that's not our job. It's our job to correct the students and not to undermine the teacher in the class even if they are wrong.