I just realized Elaine is training a designer - not a framer.
From my perspective, that's much harder - both the training and the learning. It's not just a matter of "I'll show you, then you try it, then you practice it." Every job is different. There's also not much room for my "one-job-at-a-time" approach, unless you can use a designer who specialize in glazing, for example.
This is an area where one of those "pre-visualization" software packages can be really useful. My daughter spent a lot of time with the Wizard package (Virtual Frameshop?) designing mats and frames for a variety of images. She'd put together packages on the computer and, when she was happy, we'd talk about what she'd done. Sometimes, we'd pull the actual mat and frame samples and, in a few cases, build the whole package as designed.
I also have several customers who will leave projects for me to design at my leisure and I'd let my daughter work on those for practice. I was able to incorporate some of her ideas and it was good experience, without the pressure of working face-to-face with a customer.
It's also useful, I think, to set some general guidelines, like you'd prefer that the mat be wider than the frame (if that is the case.) This is also very hard to do without being overly restrictive, but everyone has to start somewhere.