A family history report makes a great writing unit for middle schoolers since they are likely to be very familiar with their own family. This topic gives them an opportunity to exercise both research and self-reflection, two key principles for effective writing. Have them trace their genealogy back a couple of generations, at least to their great-grandparents, and conduct an interview with an older relative.
Tell the students to come up with a specific task, chore or activity that they are personally familiar with, such as juggling a soccer ball or baking cupcakes. Have them write a short essay explaining the activity, step by step, in a clear and effective way. They could then read their essay to the rest of the class, perhaps getting a partner to perform the activity as they recite how it's done.
Instruct the students to draft an essay, whether it be persuasive, informative or instructional. Divide the class into peer review groups of two to five students each. Have them exchange their essays and respond to each other's work, discussing the pieces as a group and writing a brief constructive critique.
Present a piece of art to the class -- a painting, poem or selection of music -- and have the class write response essays. Have them include what they admired about the work, what they didn't like and what they think the artist was trying to present to the audience. For middle schoolers, choose a healthy medium between something too challenging and something that will bore them to apathy; a Picasso painting or a Chopin sonata would be ideal.