My children tend to be pretty honest people. It sure makes life easier as their parent, and I try to remember to count my blessings on this, as on so many other, fronts. The other day on a message board someone asked about discipline strategies for lying for her friend's 8-year-old, and as I wrote my response (quoted below) I had a chance to think through what I do, what I would do, and why.
"Do you ignore it, do you take things away?"Neither. First, I'd examine why my child is lying... wishful thinking, inappropriate expectations, fear of punishment, impulsiveness, a desire for increased autonomy and control, etc.. I'd try to deal with the root causes.
I'd be very careful to phrase my comments to my child in such a way that they don't encourage lying. So rather than saying "do you have any homework?" (which invites a child to say "no") I'd say "let's get out your schoolwork and look through it so we can find out what should be done." Rather than asking "did you eat the extra muffin?" (when you know perfectly well he did), say "I see the extra muffin is gone. I would really appreciate it if you would ask me before snacking on the baking because sometimes I'm counting on those things to put in your lunch the next day." I think lying is always tempting to children, because if they can pull it off it's such a quick and easy way to avoid conflict and to avoid facing stuff about themselves that's hard to accept. So it's important not to let them develop the habit of lying -- by minimizing the temptation.
I would make sure it is very clear to my child that lying is not acceptable. Not by punishing, or arguing over what the truth is, or by getting angry and telling him off when I think he's lying. In the heat of the moment I would just move on. But later, when things have cooled off, I'd take a quiet moment with my child to say something like "That episode this afternoon with the muffin really bothered me. I hope you understand that it's important for you to always be honest about things like that. I'll find it hard to trust you about lots of stuff if I can't count on your honesty. I know you're a good kid and you'll want to do what's right. Can you be a little more careful about that tomorrow?"
And obviously if, despite such efforts, lying continues, the logical consequence is a loss of trust and an increased need for direct supervision. If a child, for example, continually lies about having brushed his teeth when he hasn't, the solution is to accompany him to the bathroom to watch him do it. If a child lies about using the family computer when mom is napping after night shift, she'll need to sleep with the power cord.