Bruce,
What you say is valid. I've read 20 minutes is the maximum time people stay interested in learning-related information (not entertainment-related). I don't how true, but frequent change-ups from one activity to another, to another will help keep an upbeat, flowing stream of new inforation that keeps the students interest and focus. Or, as you imply, a short story related to the course or career area will often reengage distracted students back on topic.
Regards, Barry
