OK, this is a rather lengthy paper, and I thought I would have gotten through it by now, but I just don't have the time. So instead, I'm just going to mention it here and let you people read for yourself.
This paper seems to argue that in cases of supporting diagram that accompanies a physics question (not diagram that actually is essential to the question), this diagram can often be useless, or even a hindrance to the students' ability to solve the problem.
This isn't the same as the student having to draw a diagram in solving a problem. That is not the subject of the paper here. I'm still trying to understand what is actually categorized as "supporting diagram" that accompanies a physics question. Maybe once I have a hang of that, the rest of the paper might be more relevant.
Still, if you're bored, you might have a go at it first ahead of me.