They weren't paid all that well either. Most of them could be seen working various odd jobs in the summer or other times school was not in session. One of our best music teachers found out what the district was paying sending musical instruments off to Minneapolis for repairs. He offered to do them in his basement at a fraction of the price.
He was so good that, next thing you knew, neighboring school districts started sending their instruments to him as well. He ended up retiring from teaching and going into the business full time. His timing couldn't have been better. For it was about that time the NEA got salaries pushed up along with a lot of bs restrictions on hiring and on allowing teachers to do outside work. They wanted them beholden to only the union.
I recall 30+ as the norm circa 1960. Basically 6X5 desks in a room with a partial 6th row.