What a great project
I have succesfully built two online schools, been running one of them for 2.5 years with almost 3000 users in a very specific industry, we find that people love tasters, they love to know up front what they will get.
Perhaps a tour video, showing a logged in user.
And I agree with the others, getting hold of those influencers who service your target market and may want your course to add value to their offering or be happy to test and recommend out.
You can’t give away your course for free to all the time or long term to anyone without diminishing the value, in my view, but to a few key influencers in light of getting the word out to their parents or adding to their own offerings

You can do affiliate options, so people can get a cut if they promote your course too.

Word of mouth as well as digital works best in NZ

If you find something catchy and thought provoking speaking the direct language of your target market, talk benefits (whats in it for them) rather than features and then you can create some low cost but effective social media marketing

Facebook is great for this demographic