My mom is a special ed teacher. Don't quote me, but I think how it goes is that bare minimum you need is a reg. teaching degree and state license. Most places require the degree to be in special education, quite a few require a master's degree in special ed beyond that. I think in places with teacher shortages and stuff you wind up with situations where they only require the bare minimum.
My mom teaches students with severe emotional behavioral problems. It's definitely a challenging field and takes a special kind of person to do it. Even dedicated people tend to burn out after 2 years. I know when she's mentored teachers doing their practicum portion she's had some that she thought shouldn't graduate, even expressed concern that they weren't the right fit for those types of positions but they graduated anyway. Schools seemed concerned with graduating people more than anything.
I've spent a lot of time in her class volunteering and in the special ed room next door with the students dealing with autism and things like that. Most of the teachers and paras (aides) were incredibly kind and patient people who truly loved working with these kids. There was this one woman working as a para though that was a real problem. My mom had commented a few times that whenever she left the room, she'd come back and this woman would be getting after someone who'd been fine just a few minutes before. She thought it might be more an issue with the aide than the student. So I was out there one day while home from college and the students were behaving very well. My mom stepped out of the room to answer a phone call and almost right after she stepped out, this para starts in on this kid, pretty much just harassing him and trying to get a rise out of him when he'd be quietly working on his worksheet. I'm pretty even keeled but I was about ready to lose my cool just watching her, so of course the kid starts getting upset. It was clear the woman enjoyed the power trip. I asked her some questions and tried to distract her so the poor kid could finish his worksheet. My mom came back and I had a little chat with her about what I saw. Fortunately the woman didn't last too long after that, but I think you wind up with a lot of people who enjoy the power trip and having a group that they can boss around more than the teaching aspect. It's really sad, because even the really challenging kids are rewarding to work with.
I know for awhile they had trouble trying to staff people in that classroom too, my mom finally said she'd rather work short staffed with a good team than have an extra body with someone who was terrible with the kids.