I don't know your child, but I can say that a toxic school situation beats almost any level of new-situation-anxiety-- and honestly, if what your child has reported is true? THAT IS TOXIC; this is a teacher taking what YOU told her, adult-to-adult, and twisting it into punishing HIM verbally in ways that would be unwarranted even if he were being unmotivated in class.
I don't see this situation going anywhere positive without a lot of administrative pressure and a firm talking to about keeping things professional when a parent contacts the teacher with possible concerns.
Depends on what you want to do-- but I'd be afraid that the jabs at him would just be on the sly and you would learn progressively less about them as time goes on.
I'm cynical about this kind of thing after so long, though.
