You have the right idea in getting students to work in groups; it’s essential in dealing with large classes; it will take the focus away from you the teacher and get the students working together and autonomously.
At the beginning keep groups the same to minimise the time spent getting into groups, it will also help students feel at ease if they have not studied in this way before. Later on, you can vary the way you organise groups: this will prevent students from getting complacent and over-familiar. Sometimes put all students of the same level together and sometimes have different levels working together. Your role is to monitor the groups to check everybody is participating and speaking English. Try to avoid getting involved in long conversations with one group because you won’t see what other groups are doing. Note any problems that come up as well as examples of good work. As time goes on, you can appoint some students as group monitors: they are responsible for making sure everybody contributes and everybody speaks English. The role of group monitor can rotate; it doesn’t have to be the same person each time.
It’s important to have good discipline in large classes; this is where your classroom management techniques will come in. Establish rules with the students at the beginning this will include speaking English, speaking quietly. At the beginning, establish routines: use signs to manage the group; have a sign that everybody understands for getting into groups; to stop speaking; etc. It’s important to decide at the beginning how you will deal with students who finish quickly. Have something up your sleeve for students who finish early; this could be exercises from their workbook, doing homework (make it sound like a treat; i.e. students don’t have to do their homework at home). You could have an early finishers corner where there are exercises and / or books. Make sure that students know beforehand what they can do when they finish; this means you won’t have to explain it repeatedly.
It’s also a good idea to be available to the students. If you can, turn up early to class and stay around a few minutes at the end: this will allow students who have problems and / or are shy to approach you. You could also set up a place on internet where you can post instructions for homework, messages for students, etc. You could also have a suggestions box in your classroom or on the website.
A few final comments: have a contingency plan for mixed ability; Try to cater for different learning styles – there will be a variety in a large class. Variety is essential in large classes; try to vary the activities. There is nothing worse than a group of 35 bored people!
Please also look at my response to a similar question on 20 September 2005.
All the best,