They want to be independent.
The drive for independence really ramps up in second grade. Children this age are immersed in their school life, becoming more social, withdrawing from adults, and have improved logic and reasoning to help guide them. They are starting to build an identity, which is a long, complex process.
What you should do: Be supportive and open-minded. Your child wants to create his own identity, not one that you create for him.
