This varies by field and level. I taught high school science for a few years, and in my state they were so desperate for science and math teachers that they were taking people without teaching certificates, and letting them get certified while teaching. I felt bad for those folks, by the way - they were often wildly unprepared and though they were well educated in their subject area, they hadn't the vaguest idea how to teach it or manage a classroom.

I had a BS and an MS in the field I taught, and I took an additional year and a half of teaching courses (they weren't hard, but they weren't a waste). While this certainly wasn't required, you were required to have essentially majored in your subject area in order to qualify to even take the certification exam. I certified for "Composite Science," which most science teachers in my state do - it required 24+ credits in your main area, 12 in your secondary area, and 6 (or more) each in two other areas. For me, this was Biology, Chemistry, Physics and Geology. My certification test covered all of them and was a fairly legit test.

I still made the same bullshit amount of money. I made a whopping $800 more a year for having a master's. I knew this would be the case, of course - no one goes into teaching to make money - but I got tired of being underpaid, buying my own fucking copy paper, and being disrespected my idiot good ol' boy principal who really wished I'd just skip the evolution part of the curriculum. When I quit, there were definitely not 140 science teachers around.

I didn't leave because of the kids, or the money, or even the dickhead in the front office. I left because I got worn out of spending 60-80 hours a week pouring everything I had into my job, only to have people tell me teachers have it easy bc work is "over" at 3:30. I left because my district would conduct "professional development" about making sure you smile and have a good attitude. I left because in every disagreement with a student, a parent, or any asshole off the street, the teachers were never given the benefit of the doubt by administration.

I don't know if I'd still be teaching if this thing or that thing had been slightly different... The career I have now (I got a second masters) is awesome, I make almost triple what I did teaching, and I'm quite happy doing it. I don't, at the end of the day, think it's as important and sometimes I feel bad about myself for leaving the profession. I wish it wasn't martyrdom or nothing.