I'm a former STA employee. Haven't worked for them for a long time, but this is my experience with them. YMMV.
They're a private school bus company that specializes in transportation of special education, though they also do general education transport. They underpay people and they also hire and train the lowest of people because that's what costs the least. My location was union, and I don't know if there are any that aren't union. We were run by the Teamsters who were just there to collect money from new hires and not actually help any employees. They were in bed with the manager.
For special ed transportation, the driver is not given training in how to deal with medical problems, and neither is the bus aide. My bus aide didn't even speak English! Generally, the bosses just pray that nothing happens on a bus.
I did have students being abused on my bus, so I submitted reports, as we were considered to be mandated reporters. My boss HATED ME for this. Where I worked, they reported directly to the county education board, rather than the local district. Literally nothing happened after my reports. I don't know if my boss refused to submit them, "lost" them, or if she was in on something with someone at the county. Either way, nothing happened. This student was given to me because of her severe stubbornness, and no other driver wanted her. Since I was lowest on the seniority list, I got to transport her. She actually became a good student on my bus, thanks to God.
Jobs are low paying and are all part time; I don't know of any divisions that had full time employees, except the office staff. The mechanics were overworked as most of our vehicles were old and should've been retired ages before my employment. There was also a lot of employee abuse at my location. I've heard other locations were better, but that's only rumor to me.
If STA didn't hire those Brown Bus drivers and make them the most senior drivers on their list, then this was a political play with someone in the local government signing off on it. I would then assume that this is a way of "dealing" with your local kids. They won't talk to your kids like a normal driver will, but they will berate the fuck out of them.
That's my $0.02. My apologies for no tl;dr.