just to ruin TooHasty's theory I work FT, I am a SP and my DC 7& 3 (been with CM FT and after school care etc since 8 months) are usually pretty well behaved. Certainly in "public" they are usually pretty well behaved, respectful and aware of other people I'm often complimented by other parents on their behaviour.
At home can be a slightly different story, but I find setting boundaries and being consistent the key. They never do stop nudging at those boundaries though, but I really wouldn't want them too (I don't want to grow overly compliant people).
I do talk to them about when is time for fun and being cheeky and when isn't - I don't want endless hassles and mischief at certain, mainly functional, times like getting dressed, brushing teeth, getting ready for school/bed, getting to car etc. So I will be more serious and strict at these times - and I let them know there is a job to be done.
But I can be much more relaxed/silly/accepting at other times so it all balances out. If I had to be 'fun' mum involved in endless shenanigans at bedtime every day, for example, I would be on the brink of madness.
I also let them know if I am over tired or not feeling very well - and ask them to do extra good listening, be supportive etc, and they usually get it.
I have friends who go down the "please darling sweetie do what Mummy asks" route of communicating with their DC, and their children usually respond with a blank face and then continue fighting/not listening etc.