In anything. Like math, or math education. I was a teacher for years and studied education and I've seen some shit. The acceptance criteria for education degrees is often the lowest of any field in colleges/universities. The pay is extremely low. Great teachers exist, but often teaching is just a backup career for non-experts that don't know what else to do.
Outside North America teachers are sometimes respected and paid as professionals like a doctor or lawyer. Here they're more likely the butt end of a joke. You don't need to be an expert in anything to be a teacher in NA, generally.
Experts in what, grade school math? Do you mean professors?