I'm not very convinced the learning curve is too steep, I have always found LaTeX to be quite intuitive. I have recently given LaTeX assignments to my students, and they have taught themselves LaTeX with almost no problems. Sure, these are university students, but it shouldn't be that more difficult to high school students.
Here are some things you could do to easy the process:
1) Clearly tell them the steps they need to follow to install LaTeX on their computer. This can be confusing for many students.
2) One of the hardest parts of LaTeX is writing the pre-amble. So I think it would be best if you would create for them a generic pre-amble that they can use for their first assignments. Later, you could always teach them how to modify this to suit their needs.
3) For their first assignments, give them a very basic list of commands to use. For example, check the table on our FAQ post:
https://www.physicsforums.com/showpost.php?p=3977517&postcount=3 Give them a few assignments to get used to this, then start doing more involved things like arrays and matrices.
4) Practice makes perfect, so encourage them to do some homework assignments in LaTeX.
5) Aside from the LaTeX, scientific writing is an art and there are quite a few rules. I really like the following document:
http://www.math.washington.edu/~lee/Writing/writing-proofs.pdf The title says it's about proofs, but it applies far more generally than this. Be sure not only to give feedback on the LaTeX code, but also on their scientific writing style.
6) Also, give them an example LaTeX document that uses all the tricks and commands that you think are important.