Maybe it would be helpful to suggest some alternative redirection ideas to the teacher when she says this. While it may be awkward you should defend the students by stating your opinion that you do not think the students are bad, they are children after all, but that when she makes these comments in front of them it seems to only encourage their negative behavior.

A teacher should never talk about students in front of their students or anyone else for that matter. If the question is how can the teacher quiet down and get her students attention.There are many ways of doing it such as using hand signals or attention grabbers like the teacher says “Hocus Pocus” then the students reply “Everybody Focus! or the teacher says “No bees, no honey students reply “No work, no money!” The teacher should also create and review classroom rules and procedures every single day until they become routine and inform her students of her expectations before transitioning into a different parts of the day.

There is a difference if she said " they are bad students" or "they are acting bad". I understand her frustration on not having students talk over her but she should try to control her anger. It is hard when you are a guest in someone else's classroom, but take a mental note of this since you see how it affected her students.

I would start by discussing with the teacher that not all the students are bad and that they just need a little redirecting. By her saying this statement, this is degrading and will eventually allow all of her students to believe that they're actually bad.

I agree that the teacher seems very overwhelmed but that is never an excuse to call children bad. I would work together to find things that work best in your classroom. Maybe come to her with a few suggestions during one on one time. I would suggest talking about it at a minimal stress time.

It could definitely be an awkward situation. However, I would take mental notes on how the class acts before and after her comments, and use that to help use different words to get better results. Trial and error

Children are not perfect. I think they need someone to advocate for them and believe in them. Children are greatly affected by the things we say, especially negative.

There is no question posed in this case. What are you looking to accomplish?

I would suggest to this teacher that she should consider a different mindset. There is something called the Pygmalion Effect. According to the Pygmalion Effect, how you feel about your students will affect how they behave and achieve in your class. If your teacher has a defeated mindset towards her students, they will continue to display dismaying behavior and fall behind academically. I do not know how to motivate a person to think more positively, but a positive mindset is necessary for this line of work.

Hopefully, she is not telling the students in front of them that they are bad. The teacher seems overwhelmed. Maybe you can come up with new ideas for her to try when settling the class.