Hi! I wrote out a response yesterday and lost it, so frustrating! So I'm back and basically was going to say what others here have said.
So, first I'll start with you. Yes it feels crazy making when people dont see what you see and also when they try to "help" and they use traditional methods (in my circle they try to use logic and appeal to his sense of right/wrong....you dont talk to your mom like that! blah blah, it only makes it worse for me in the long run). But for sure we believe you and a good neuropsychologist should too. (I just met a mom with twins who had a neuropsychologist say the traditional things about them needing to be better parents etc. and it turns out they are autistic! Luckily she is in a good place now but of course if it does not hit as true in your gut, even a neuropsychologist can be wrong once in a while. But compared to other options this in my experience has been the best for the "big picture" and helping to sort out how my son learns, what his strengths are and what his weaknesses are. They make good recommendations for therapies too and that helps with insurance and can save you money in the long run even if you have to pay out of pocket for the evaluation.
Bunny is right, it is often true that our kids fall apart at home. That never was the case for my son until recently. He has had days like that. He typically fell apart everywhere but as he is improving in some areas he does hold it together in many settings then it all pours out on me.
Another reason he may be dong well is that in school, espeically once elementary starts, they have a pretty consistent schedule/routine and the schedule is often on a board and visual so it is quite predictable. Even if there are changes they often prepare the kids in advance for those changes by changing it on the board.
So, you may want to start creating a routine and using a simple picture schedule that can be modified easily (like a pile of pictures that you can stick up in a line from top to bottom taking each one off when done or a white board where you erase the little symbol/picture plus word you use to say the schedule. Even if they can't read, reviewing the schedule with them helps them to settle into the day. Being fairly consistent on weekends is hard but well worth it.
Not that you can't vary your days...just have a schedule and review it (and, yes, there are kids who get anxious if they know something like a dr appointment is coming up or too excited if a fun event is coming up and you may need to NOT tell too far ahead of time for those situations, just present it still in a visual way a short time before the event). Routines like for example a bath routine may include a washing song while you set it up so she gets in the right head space...same for breakfast or cleaning up toys etc. can help tremendously. I used pictures (like a photo of our car, a picture of eating for any eating situation, a school bus picture, a tooth brush picture, etc....) and put them on a ring for each day...(they were laminated with holes punched in the corner). Each day I could change them around if I needed to. My son would flip the picture when done with a step. We would go through the whole "story" at the beginning of the day. You might use whatever is close to how they present a schedule in the school setting as a model if she is doing well with that. It is often also helpful to give a countdown to a transition ...which you can also do visually by having numbers on cards. You can show a three and say three minutes and we go (you dont have to really watch the clock, minutes for me were sometimes seconds and sometimes longer than a minute but just make sure you stick to the count, dont start then stop then suddenly pull them to another activity like "get in the car, we are late")....then two then one then go...it often helps. A transition song can help to....just make one up and use it for every transition (take a tune like ABC song and sing "now its time to go to bed, lets get ready sleepy head" (hey that's catchy, lol).
Also, kids sometimes do really well in school and look like they have no issues there until about third/fourt/fifth grade. Some wait till middle school to fall apart in the school setting like at home. The language, social challenges etc. increase dramatically at those ages. It is super frustrating for parents who know there are issues and have kids who appear to have no issues in those early years because we all want to intervene early to help head off the issues we know may be coming. Unfortunately if they are not impacted in the school setting you often have to wait for help there and use private sources who also may not believe you and may say it is a parenting issue if it is only at home. But you KNOW in your heart if there are bigger issues and there are ways to address them. ODD really only says that a child is behaving in an oppositional and a defiant way. OK great, many many of us here have kids who fit that. As you have found, it helps very little in a practical way. The only thing to do is to dig and dig to find out how your child is experiencing the world. How does he see, hear, feel, process everything? Does he have neurological conditions like a learning challenge or Autism Spectrum Disorders (ASD) or any number of issues or does he have chemical imbalances like childhood bipolar etc.... those bigger things may be hard to figure out so looking as well at what situations trigger him, what consistently calms him, does he seek tons of input at home like touching things or making noise? All those things are issues to sort though that can really help when you try to give him the skills he needs to do better. Most kids do want to do well and are not loving life when they are being oppositional. Most kids (not all but yours doesn't seem to fall into this small group as far as you have presented so far) do well when they can! It is really helpful to read The Explosive Child by Ross Greene and/or What Your Explosive Child is Trying to Tell You by Doug Riley to help give a method for looking at what skills he has or doesn't have and how you can fill those in so he can for example tolerate frustration better, or be willing to wait for things better etc.
Glad you are here!