to write mainstream/literary fiction. I see some really dull settings.
And I mean dull.
Also some unoriginal plots. For the first assignment the students have to write a story from the POV of a child set in a city street where something has just happened. In any one batch, I can bet that 50% will be road traffic accidents.
Christmas is an especially bad time. The numbers of parents and dogs that were run over in the batch I marked around then was amazing1. The low spot was the story in which Santa himself went under the wheels of a lorry.
But having said that, I vividly remember one stunning story that captured the child's viewpoint brilliantly and was scary and touching without being sentimental. So it isn't always the plot and situation. The writing and how the idea is handled counts for a lot too.
The students aren't actually told to write a mainstream story. Most just want to write that kind of fiction. There's nothing in the instructions to prevent them having the viewpoint child be a slave in Ancient Rome or a young noble in the high fantasy city of Var Thionin or a young N'drissi on the planet Thooongg witnessing the aftermath of the attack by the Druuugs. Whether they want to write mainstream or SF, it's going beyond those first thoughts that counts.
But having said that...
The first thoughts can sometimes be the weird ones. The danger then is they get rejected by the Inner Rationalist who wants everything to be dull, comfortable and realistic. I have finally managed to stop the Inner Rationalist sitting on my Wild Mind2 and shouting her down when she comes up with ideas. This is why I have a flying mountain in the WIR. The Inner Rationalist didn't like it one little bit, but the Wild Mind won.
 The dogs sometimes survived; the parents never did.
 Natalie Goldberg's term for the spontaneous, unconscious mind that tosses up all the weird ideas. (See Writing Down the Bones)