Welcome to adolescence! This kind of behavioral change in preteens and teens is why it is so important to understand development. You can learn more about human development and individuation (which is what your son is going through) by reading my parenting book.
During the teen years, the brain wipes out entire neural networks and reconstructs itself, giving rise to the complex structure that is the prefrontal cortex which is responsible for our ability to make good choices. This is why a formally sweet, responsible child can seem to transform overnight. This is when parents begin to see all kinds of teenage behavior problems.
Your son may also be experiencing the surge of testosterone that is the hallmark of puberty and is responsible for mood swings and aggression. At certain points, your child has 1000x more testosterone in his blood stream than he had as a child. This takes some getting used to.
That said, use this information to help you understand what he is going through without giving him excuses for poor behavior. You just need to get through this period, even though this is easier said than done.
However, it is important to know the difference between occasional bouts of anger, defiance and disrespect and chronic disrespect for authority, which can be a sign of conduct disorder or oppositional defiant disorders, two diagnoses that are on the rise.
To learn about a behavior program that can help turn around defiant teens and adolescents, read my review of the Total Transformation. It is an excellent program for kids with teenage behavior problems that seem to be getting worse with time.
It is also a good program for parents who grew up in overly permissive homes and don't know how to draw boundaries for acceptable behavior that are respected by their children.
