I haven't read the responses.
Our son is 6.5. The disrespect overflowed. I don't believe in punishment. I do believe in GD.
What worked (out of desperation) was to make him earn what is dearest and nearest to his heart--computer time and desserts.
We homeschool and he spends his sister's naptime on the computer (usually how it's made.) He also is a sugar addict (though he only gets one sugary food a day.)
Quickly we learned that having to work all day to earn something in the evening did not work. It was too long and theoretical. So we started the day working towards afternoon computer time. He needed to be respectful and kind to earn the computer. Then second half of the day was spent earning dessert. If he did something that kept him from earning afternoon computer he immediately started working on earning dessert. It didn't take him long to turn into a rather polite child and the whole earning "rule" went away. Though we randomly bring it up if his behavior is getting borderline.
In some ways this is like punishment in that we are taking away a privilege, but it does come out more pro-active in practice. He is working to earn something.