For a discussion on source criticism in an upper level Torah class, I provided a email from me to my dissertation supervisor from late in my PhD program. The email had several quotes in it from different readers on the committee which I was responding to (without providing quotation marks).
I had stripped away dates and replaced last names with first names only. I then asked the class in their groups to deduce as much as they could about authorship, date, topic, sources, etc.
I made the exercise competitive (the winning group was excused from a forum post the next week).
It worked well, a few groups noted quotations and changes in tone (even when there were no quotation marks). Some even made some presuppositions about motives and a couple even figured out some of the people involved. It drove home how hard it is to work with a composite text when you don’t have access to the other sources involved.
I imagine an exercise like this might work well for a discussion on epistles in New Testament as well.