They seem to understand everything and some of them act like they have nothing else to learn. At the same time, you can really get into the nitty gritty of the language by teaching them slang, idioms, and such things that are difficult to teach less advanced students.
Keep Track of Progress
With advanced students it's hard to see that they're making progress. Have them keep a journal or a list of goals that they want to accomplish by the end of class. If they want to use a certain idiom, they should jot down when they use it.
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Formal vs informal English
Usually one will come easier to them than the other. If they can easily use informal English, challenge them to take it up a step and be more formal and vice versa.
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