Unions are optional in Texas and are generally powerless here.
Even teacher’s unions?
Yep. Especially teacher’s unions.
My guess is that maybe this “teacher” is a coach. Too many coaches are asked to teach other subjects that many of them are not qualified to teach, IMO. The only exception to that I ever saw was my high school algebra teacher. Smart as a whip and knew his stuff. He was also the basketball coach. He moved on to become principal and eventually school district superintendent.