Hi,
I think that this poor analogy, the premises of both situations are entirely different.
To begin with, we do not know for certain who wrote any of the Gospels, I assume that you would know who wrote your students essays.
Next, The Gospels were written anytime up to 80 years after Jesus died, I assume you havent given your students that long a deadline.
Next, all your students were present at your lecture, not all evangelists were present at these events. Mark did not know Jesus, Luke ceratinly didnt know Jesus, there are major disputes whether Matthew's gospel was written by Matthew Levi, and John's Gospel is far too late to have been written by an eyewitness.
Next, although you would expect the stories to be similar, if any of your students handed in an essay that reproduced many sentences identical in places to ther students then you would surely query it, I certainly would.
Also, in the Gospels there are stories about events that no one else was witness too, the temptations for example, or Jesus questioning by Pilate. Ths strongly suggests that these stories were copied from earlier texts, or passed on orally before being written down.
The big problme is that 'Matthew', the only possible eyewitness, has reproduced 90% of Mark who was a non-eyewitness, why would an eyewitness do this? This is like a student of yours who attended your lecture, copying an essay from someone who wasn't, and since they fit in with the rest of the class' essays, where did the absent student get his information from?
Finally, none of the evangelists were present at Jesus birth, his attending the temple at 12 years old, and many other events, so where did they get their information from?
Brian.