Teaching basic grammar to the whole class, which would be a review for the stronger students, is a good idea (if you also later work more advanced structures into the lesson). I would also break the class into groups, with a higher-level student responsible for a certain amount of students. After teaching the grammar point, the higher-level learners would become "teachers," monitoring their group during activities, answering any questions, and making sure everything gets completed smoothly and correctly.

I've used this in my classes from time to time, but sparingly. Hope it helps.

Chris Cotter
www.headsupenglish.com