By now, most of you have heard of the movement to use “they” as both a singular and a gender-neutral pronoun. This usage is gaining traction, evidenced by it being voted the word of the year in 2016 and its inclusion in the 2017 Associated Press Stylebook. The reason to make “they” a singular pronoun is not only a way to avoid the clunky “he/she” or “he or she” sentence construction. The change also seeks to include people who don’t identify as a specific gender who don’t want to be referred to as either “he” or “she.”
For my students who I work with on academic writing, I always encourage them to seek out the teacher’s preferred usage, since the teacher assigns the grades. For those crafting college essays, I recommend that they avoid using “they” as a singular pronoun and instead suggest that they rewrite the sentence. The reason is that I wouldn't want an admissions officer questioning a student's knowledge of “traditional” grammar rules. Of course, if a student is writing about a gender fluid individual on their applications, “they” would be correct.
For me, I am embracing the “they” in my own writing, ignoring fusty grammarians, many of whom (like me) came of age under different rules. Language rules are ever-changing, and I need to adhere to the new ones as they are adopted in the wider world.