We do 2 grades together, K-6. Since we had 2 5th grades classes, we put K & 6th together. Some 6th graders will like the rotation but they are there for "mentors" to the Kindergartners, especially good if the lesson suddenly seems childish to the 6th graders.
Our 7th & 8th graders are in Confirmation class, so there is no way they would be a regular part of rotation.
Susan Johnson
St. Luke Lutheran, Portland, OR