Not sure what topic this fits in...

I have suspected my 10 year old step son might have ODD or something similar. It's hard to tell, because I also know it's hard for step children to accept a step parent as a genuine authority figure.

The difference here is almost every single time I ask him to do something he responds with either a "why?" (Even over something as routine as brushing his teeth) or he will say he doesn't need to, or he will say he IS doing it when he clearly is not.

At first I thought he was being rebelious, but then I noticed something strange. I asked him to do something slightly out of the ordinary and he almost became frantic looking for a way to do something else besides what I told him. It was as if he knew it was a simple task and was trying to just do it even though it wasn't part of his routine but he was struggling to fight the urge to rebel.

Also at school he will come home depressed because his teacher won't let him do something he wanted to do or make him do something he doesn't want to do. As many times as I explain, that sometimes the teacher just needs you to listen, he can't seem to understand. He looks genuinely defeated as he tries to explain what seems like his world view that authority figures should be letting him do what he wants. It's as if he has the understanding that he knows better what is good for him. It could be as simple as him wanting to quietly read a book to himself when it is activity or discussion time.

I can understand kids not wanting to do homework or other tedious chores, but he will fight almost anything. Examples are turning the tv volume down, putting on your shoes, throwing a piece of trash away, handing me objects from another room, doing similar small tasks in a specific order. All these will almost inevitability be met with defiance of some type on a daily basis, no matter how calmly I ask him. Also, asking/telling in a firm tone will cause him to shut down. So that doesn't work either (especially being a step-parent). But his biological mother has the same problems with him even when she is firm and consistent with him.

I don't know what to do because I want to help him, but it is also frustrating to me because it's hard not to feel disrespected when he constantly defies my authority. Also it's hard to watch him struggle to focus in school because he can't perform simple tasks.

Any suggestions?