I am District Training Chair and the CD for all of our rural councils IOLS and BALOO courses. I recently put on a IOLS where every participant could have staffed. One participant had over 30 years Scouting, many over 10 years. Most thought it was going to be boring just like what ya'll have discussed and many had an attitude that they were just there to check the box. What made the difference, as any good trainer worth their salt will tell you is adapt and overcome. Like many military personnel know you have to assess the situation and go from there. We saw what and who we were teaching and adjusted to the participants. By the end even the 30 year veteran said he had a blast and learned a few things!
Everyone's time is valuable to them. As trainers or people who are pro-training, it is our jobs to make it worth there time. No, I will not teach you how to tie a square not if you all ready know how to, but we can teach you other knots and discuss possible knot programs used in units that may help or benefit your unit.
Testing out can be a slippery slope b/c the program is constantly changing. The one thing we may teach in a course that is new to a veteran leader may be the one thing that they should really know and would not get if i just tested you to make sure you knew how to start a fire correctly.