Scratchpad, please add to and refactor!
There are a few things going on here, ... but just to focus on the skills vs topics part: to the extent we characterise it using Library- like topics, and W3C SKOS identifiers for those, we get to join up with a lot of other work, including vast bibliographic collections that are opening up, and work towards linking together different taxonomies. So the above URL for example expresses a link to the topic at http://stitch.cs.vu.nl/vocabularies/rameau/ark:/12148/cb11937509n ... giving us links into French datasets and concept labels, and in turn cross-links to http://d-nb.info/gnd/4035811-2/about/html at the German national library.
So SKOS to say "linear algebra" seems useful. But how far do the various SKOS thesauri and classification schemes and controlled vocabularies go, in terms of describing the difficulty or level of detail, or specific concept that is being taught? And how consistent are they across the board?
Or if we start from the human side, rather than just static resources? How about describing someone (a learner? a potential teacher or co- learner?) as having interest or expertise in [some specific aspect of, of difficulty-level of] some topic such as linear algebra? Can we use the same topical codes as the library community, but refine them for educational purposes? and for describing people as well as content?