My foster daughter was diagnosed with ODD when she was 8. She came to live with me at 7. And a grandson carried that diagnosis for awhile too. Both children overcame the disorder with a change in discipline techniques.
The obvious symptom is that the child refuses to obey. He's hostile and unable to accept responsibility for his actions. It doesn't matter what is asked of them. In fact, they may actually like to do what you asked but they refuse just on principal. They're mad at the world and you because you're in it sort of feeling.
What is important to realize is that ODD is not something to be cured. It is to be managed and eventually it goes away. It can be managed with the right sort of treatment which may include medication depending on why the child has adopted that sort of behavior. My daughter came from a very abusive home and had been in 5 foster homes prior to coming to live with me. It's no wonder she didn't want to co-operate with me. She did fine at school and with others with whom she didn't have an attachment issue. She was seen by a child psychiatrist provided by CSD because of my inability to deal with her tantrums.
My foster daughter was treated with counseling for both of us. Medication was not available back then.
My grandson is autistic. His brain doesn't process life in the usual way. He needed a different approach in parenting. He was evaluated by the school district initially because of learning disabilities. A social worker came to their home and worked with my daughter and him to learn different ways of parenting him.
He was later diagnosed with ODD by his developmental pediatrician when he was unable to get along in school. He iwas first put on medication for ADHD and was in special ed in a therapeutic school and has overcome his ODD for the most part. His parents have become more consistent in discipline. He is sent to his room when he misbehaves, including when he refuses to do something. He is a strong willed child and sometimes difficult to manage but a change in parenting focus has helped everyone tremendously.
The way that both children started in being assessed for ODD was thru the pediatrician. The pediatrician is able to discern if the oppositional behavior is more intense than that ordinarily seen in the average child.
It's unlikely that the only thing going on is the child's oppositional behavior if that is decided as a possibility. And, it's quite possible that their oppositional behavior is not ODD. He may be oppositional because his needs are not being met. Some children are just more difficult to parent than others and sometimes our expectations are not realistic when applied to some children. A sort of personality conflict situation. And discipline techniques work differently for different children.
The pediatrician first tested my grandson for ADD/ADHD at 3. That in it's self causes a child to be unable to focus and behave. His mother didn't want to use medication but eventually did accept it. He was in special ed and continued to have numerous difficulties. He was seen by several specialists but eventually went to a developmental pediatrician who put together all of his behaviors and care.
My grandson has a lot going on with him. He doesn't seem to be so oppositional most of the time but still has those moments. He's 9.
In summary, a child may be oppositional for a variety of reasons. It's unlikely that the first diagnosis will be ODD. Finding the reasons for the behavior are part of the process. Start with a pediatrician. Ask if a referral to a developmental pediatrician would be in order. After my experience with my grandson I highly recommend starting with the developmental pediatrician if the pediatrician sees the possibility of developmental issues. The developmental pediatrician will be a sort of case manager as your child receives evaluation and treatment with other specialists.
There are not actual tests for ODD. It is diagnosed based on the child's behavior. A diagnosis includes testing and observation of any possible reasons for the behavior. Most testing, is verbal and observational, is administered by specialists in whatever area the child is having difficulty. For example, if the child refuses to do school work it may be because he's unable to focus and that would be looked at first.
Later: What I'm trying to say is that just because a child disobeys does not mean he has ODD and that the process of making that diagnosis first involves looking at several different issues from what sort of parenting he's receiving to what other conditions may be affecting his behavior. There are, of course, children who have only ODD but they are in the minority. First take a look at the whole picture before deciding your child has ODD.
Here is a web site with information that fits with my experience. http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0002504/