As kids have started to really settle into the school routine for the year, it's likely that they're going to start testing the rules. They're going to want to know how you're going to respond when they misbehave.
Kids often feel like now that they're a grade ahead of where they were last year, they should be afforded new freedoms. It's not unusual for them to want a later bedtime or to think they shouldn't have to be home by dark.
Not to mention the homework struggles often get started about this time each year. Kids often make it known they aren't interested in doing their work every single night.
The way you respond to their attempts to set limits will make a big difference to the success of your child's school year (and your sanity). Remember, that saying no and setting limits may make behavior problems a little worse at first.
However, in the long run, it will make behavior problems better and will be well worth the effort. Check out these 10 Tips for Managing Defiance and Non-Compliance.