My high school math teacher had a completely different job during the summer.
He stayed active and that has helped him reach his 90s.
I made a fortune teaching HS for 30 years.
Well, not just teaching — I also coached baseball, officiated football and basketball, cut timber and firewood. And I invested, little at a time, all along the way.
We lived frugally. I fixed up the house and vehicles by myself, sat on used furniture, stayed married to the wife of my youth.
All of this paid off; but credit belongs entirely to God. He guided me all the way along. His principles endure over time.
Now, if a teacher wants to follow the world’s possessions and pursuits, then he/she will “look” underpaid, for sure.