Thanks for the kind suggestion Mary - Option 1 means we cant preview one topic / section sadly. So...
Option2 . Reading that helpful doc note it says "This page explains how to restrict an activity, resource or course section via user fields and/or custom profile fields." which suggests that we would have to go into each section and turn OFF the permission (ie repeating the process about 20 times - rather than just turning ONE section (I call them topics) off - is that right? If so then I guess we're back to option 0, which is to create a one topic course but that misses the intention of them "seeing" all the other topics and being curious (and aware that this is just a taster)
Perhaps I have misread the docs wrong though?
Maybe this is a good place to ask a related query, does the feature you describe permit the site admin to set a particular label within a topic/section (and thus the contents of a label) to be NON editable - but have everything else editable to an editing teacher?