Just to add – the WCs have to be on topic, but not technically correct. If the topic is “write about the sky, the clouds, and the birds,” you can write:
“The sky is green, birds can't fly, and clouds turn red during the spring.”
That is perfectly acceptable. You're on topic, even though the content is technically wrong. I received a “stronger” in my FAR WC in 2010. I wrote a long essay with a beginning, middle, and conclusion, on a topic I barely knew anything about. I even looked up the topic after the exam and thought I blew it because my answer was technically wrong. It doesn't matter. They check grammar, spelling, being on topic, and having a beginning, middle, and conclusion.