Is this a pattern you are creating or is it one that's already out there? If someone else created it, then perhaps you can find some yarns that others have used for it on ravelry.com (free to join). Just search for your pattern by name, and then look at the "Projects" tab to see who all has made this pattern. If it's one you're designing, you might still try searching for knitted capes on Ravelry and read what other knitters have to say about their experience. This can really give you some good information.
Worsted weight yarn is heavier than say DK or sport weight yarn, and different fibers will result in different drapes (often your bamboo and silk fibers have more drape, for example). I would look around at some different weight yarns and fibers and even do some large swatches to make sure this cape hangs and drapes the way you want it to, that it isn't too light or too heavy, and that the fabric won't stretch out of shape too much.
This sounds like a very important garment that you plan to use extensively. If that's the case, I would highly recommend doing lots of homework before investing hours and hours into a cape that might be either A) too heavy and likely to stretch out of shape or B) so lightweight that you float down the halls of your school more like Dracula.
Just my two cent's worth!