One great way to help reluctant writers is to encourage them to begin with something they know. That storyline will have a plot, characters, setting, etc.
Now, have them change one aspect of the plot. Write about it. Let's look at an example.
If you have a Star Wars fan, he or she will probably know the plotline, setting, and characters really well. Your student will know how the characters think and what phrases they are well-known for saying. Now they will "throw the story a curve".
What would happen if the characters from Thomas were now thrown into the Star Wars setting and plot? Can they write a well-organized piece (beginning, middle, end, etc.) while using these new characters?
Can you visualize it?
Sir Topham Hatt, "Darth Vader, you have caused much confusion and delay..."
Kind little Edward helps his fellow train-Jedi Thomas back onto the tracks by using "the Force".
My kids had a really great time with this and the possibilities are endless.
Can you picture the dwarves from the Hobbit thrown into Jane Austen's England?
What would King Arthur's knights do if their merry old England turned into Antarctica?
I have as much fun developing the possibilities as the kids!
Note: This is also a good way to connect history with writing. After learning about George Washington's strength of character and his achievements, drop him into an unexpected writing project. What would George Washington do if he suddenly found himself on the island from Lord of the Flies?