As instructors, we can potentially teach this class on a wide variety of levels and duration. Our students can be quite young or elderly - often a mix. Some students are rock solid class V boaters, others are novices. I like scenarios that require a team effort and proper use of the various skill levels at hand. This enables me to challenge the seasoned veterans (they can take the role of an incident commander) as well as the less experienced individuals. Breaking into reasonable sized teams can help ensure everyone gets practice.
One exercise I really enjoy staging is a foot entrapment on the opposite river bank in a nasty class IV rapid. I have lots of extra help to prevent any unsafe activities. This type of scenario takes lots of bodies and coordination. It reinforces a very wide variety of skills and does a great job at simulating initial confusion - something that is common in many rescues.
The classic yard sale with multiple boaters is simple to set-up anywhere and helps ensure everyone gets a turn.
I highly recommend reading the American Whitewater Accident Database for more recent incidents and constructing scenarios based on them. This keeps the course very relevant and aids in the debrief after each exercise.