As English teachers, one of our responsibilities is to ensure that students master the conventions of standard edited English, so that they will not be judged in negative ways based on their formal writing. Whether it is fair or not, others (including other teachers and future employers) may judge a construction like singular they as “wrong”—as evidence that a writer is not well trained and “does not know better.”

I tell students that they are welcome to use singular they  in writing for my class, but they should footnote it the first time they use it and in the footnote explain their rationale for using singular they.