People really only have two stories. I presently can't think of both, but the other is a Epic. An epic follows this basic scenario.
1) A young and innocent character is created.
2) This character is removed from his/her known surroundings.
3) Has varying degrees of supporting characters, Antagonist, Love Interest commonly referred to as Goddess, typically 2 mentors, comic relief who are both funny and helps direct the reader/viewer/player, and often a player who has been there.
4) Conflict takes a Protagonist far away
5) Takes a long time to complete their "destiny"
Beyond the Illiad, what follows this scenario; you might ask.
Field of Dreams
Star Wars
Indiana Jones
Final Fantasy 7, 9, 10
Mercedes Lackey's Velgarth Series.
Many MMORPG quests also follow this scenario.
There's more, but I can't think of them at the moment.
Another case and point, they follow the same components, but I don't think they classify as Epics.
X-Men and Harry Potter.
X-Men deals with mutants who are attend a school that helps mutants learn how to harness their powers.
Harry Potter is about a character who goes to a school to learn about magic.
Mud bloods living together with pure bloods/mutants living together with normal humans and both preventing those who wish to "destroy" or otherwise rule the other.
Your students are plagarising if they use persay Norrath as their world or so on, and it begs the question why you haven't taught your students to take the inspiration to create a new idea. I strongly believe that this is a cop-out.