[kisito]

Really nothing you can do. The test is on your patience. You need to keep calm and be flexible with your lesson plans. I had a class of students like that. Their company paid for English lessons which they didn't want to take. To them it represented extra working hours. So I either had absences, late coming all the time or students who were hard to motivate. It tests your nerves.

[jakda]

You can always change your lessons to accommodate those who turn up late, but it isn't fair on the other students. Talk to them individually and explain that it affects others you, and the other students who turn up on time.

They may have reasons for turning up late, but if it is just down to lack of effort to come to class then it isn't fair. It is always harder with adults as calling parents makes a big difference. But beschar offers good advice. Keeping a good relationship within the group makes it harder for those to break the cohesion. Let them know that.