What did it for me was a combination of 2 things, repetition and large scale seeing the cast on stitches and knit stitches being formed.
On diynetwork, there was a show (the videos are online) that showed long tail cast on. The instructor used large dark colored wooden needles and a very thick bright pink yarn. The contrasting colors made it VERY easy to see what she was doing. Unfortunately, though she didn't do as many cast ons as I needed to catch on.
What really drove it home for me were in Amy's videos where she keeps repeating the stitches over and over and over so I can really get a concept. She's also got the close ups, and she goes in slow motion instead of knitting at 90mph like I've seen some folks do in other videos.
Now, that's just for me...you would need to consider what kind of learners you have. Do they learn better by having something explained with words (audio) or do they like looking at pictures with captions explaining the pictures (audio/visual) or do they like to watch things being done a few times and then trying it on their own? And then you'll have the rare person who needs all three (moi).
If I need to learn something completely new, and I don't know the terminology I need to read about it, have it explained to me a couple of times, shown to me and then I need to try it myself. After that I pretty much have things down pat!
You also might want to sit down right next to them and ask them to try a row or two of whatever stitch is givng them trouble so you can see exactly what part of it they are having trouble with. You might just have a 'knitters language' barrier!
Hope this helps you!