How commercial is "non-commercial"? A reader asks ...

One of our readers has written to this weblog to ask about the position under copyright law where teachers seek to use Creative Commons non-commercial (CC-NC) images in a lesson in which students are actually paying to attend the class. Says our reader by way of personal opinion:

"The use of the image does not seem to fall within CC terms of “primarily intended for or directed toward commercial advantage or private monetary compensation” -- but there could be different interpretations. In the United Kingdom as in other countries, many educational organisations now need to charge for attendance, including universities. The only definitive advice I can find is in this document ["Free Knowledge Based on Creative Commons Licenses" by Paul Klimpel] with a German viewpoint from 2012 which advises on avoiding NC licences".

Do readers have any ideas or personal experiences to share with our reader?