Unfortunately I agree. I had only one teacher who knew I was transgender at the beginning of the school year, and it was incredibly confusing for all the other teachers. I came out to the rest of my teachers all at once (or, within 2-3 days). It was terrifying- but generally if they call cisgender kids by their nicknames, they have to call you by your preferred name or else it is discrimination.
This is how I told my teachers:
"Hey, Mr./Mrs./Mx. ____, can I talk to you about something? I came out as transgender during the summer, and I was hoping, since you call other students by their nicknames, you'd call me Avery?" Typically I got positive responses.