Your child now wants more independence. They wants to make decisions for themselves, do things on their own and wants to have more control over things in their life. For example, once they finish their homework, they will decide to watch TV. They will try to plan their homework starting with the subject they like. At the same time, they can take wrong decisions, or make mistakes which can cause frustration and disappointment in them.
As a parent when you try to correct them, they may express defiance, talk back or start whining. For example, when you tell them not to do something, they may come back with a declaration, “You are not the boss of me!"
What you need to do
Laying down firm consistent rules is very crucial in inculcating the desired behaviour in your child at this age. Make your child understand what sort of behaviour is expected from him both at home and in school. Communicating rules and the expected behaviour beforehand will help in getting the desired result.
When your child is upset, listen to him but avoid engaging in long debates. When things get worse, disciplinary actions need to be enforced. Disciplinary actions can be something like taking away his privileges of watching TV, playing video games or not allowing play dates. For example, one of the rules that you may have set at home is TV watching for 1 hour. Explain the consequence to your child: if the rule is violated, the channel will be locked. Be sure to stay consistent when enforcing the rules. Don't waver from your decision. Also explain to your child that watching TV for long is harmful to the eyes and health. As your child grows, more conflicting situations will arise. Establishing firm boundaries and clear expectations from the start will reduce/eliminate behavioural problems.