When in doubt, ask an expert, in this case a self-identified genderqueer advocate (their word - ‘their’ in the singular, as explained below).
"My fifth grade teacher always told me that using “they” as a singular pronoun was grammatically incorrect. Is my fifth grade teacher wrong about that?
While I’m sure your fifth grade teacher meant well when they were teaching you the rules about pronouns, the rules you learned in fifth grade are most likely outdated by now. In fact, the 200 linguists at the American Dialect Society declared the singular “they” the 2015 word of the year. Merriam-Webster and the Oxford dictionary both also include the singular “they.”
Whether your fifth grade teacher likes it or not, “they” is now a recognized and grammatically correct singular pronoun.
Also, I don’t know the gender identity of your fifth grade teacher, which is why I used “they,” rather than “he or she.” Not only is “they” a more streamlined option, “they” also allows room for the possibility that your fifth grade teacher didn’t identify as a man or a woman at all! Maybe they were genderqueer. Maybe they were nonbinary. I don’t know their gender, so I’m not going to artificially limit your fifth grade teacher’s gender identity to one of two options. It’s a more inclusive, fabulous way to go about it."
There ya go, if you want to be fabulous, this is your roadmap. The map goes all the way to Canada apparently.