I've been in this situation many times and, of course, there's no easy answer, otherwise it wouldn't be such a common problem.

It's probably worth working out why students won't speak (in English) in class, because that can give us some clues about what we can do to help.

Sometimes, it's because there is no 'culture' of speaking in the class - the teacher has always done most of the talking.

Help by starting to get the students to use English for the little things they do in class. For example, asking questions in English.

Check out the classroom language section in Go! and make sure your students can actually say these things when they need to.

Perhaps it's embarrassing to speak in front of their friends.

I know I felt like that at school when I was learning French. Here are some ideas to try.

Give the students English names and ask them to become that character when they speak in English - this way it isn't so hard to say something incorrectly. Help the students to say something that they really want to say - something real and not just part of an exercise from the book.

They haven't got any confidence in English.

Two things can really help here. First, give the students simple things to do to begin with, so that they get the feeling that it's easy and possible to say something and be understood.

Second, give them encouragement ("Great, well done, I understood that!") instead of immediately picking up their mistakes. This way, you can help the students to feel the pleasure of saying something, before they get stuck with too much thinking about accuracy.