I went through the courses and found them scattered and a bit confusing.
Reviewing the PMBOK chapter 5 (Project Scope Management) was comforting after all that. I'm impressed with the organization of the information; in the end, though, it's exactly what I've been using since my early days at IBM. Understanding the requirements, getting buy-in, and putting a process in place to control change are the cornerstones of the process, as my experience has shown them to be in real life.
For those of us old-timers, WBS (work breakdown structure) is just a new name for a familiar breakdown of work, with progressive elaboration (isn't that a nice neat term?) for longer/more complex projects that need to go a step or two at a time.
It's true that many agile projects are designed with change management as part of the system - that's the point of an agile process; however, the change management still occurs during every iteration. We try to keep all changes out of the iteration, setting the barriers to entry high, but sometimes things change faster even than an iteration. So the process still exists, but the terminology and timing are a little different.
All in all, this is pretty familiar territory and I think any experienced project manager will find the PMBOK organization a handy summary of the work she does on any given project.