TIP
My older daughter sucked her thumb, while my younger one used a binky. I was able to wean each of them from their respective habits within a day. Yep, you heard it — cold turkey, all at once, in a single day. While I make no claims that I caused no psychological damage, but I will say that I used the most effective tool available: The Truth. The conversations went something like this:

Me: If you keep sucking your thumb, you’re going to need braces. [using a tone of voice usually reserved for ghost stories] Do you know what braces are?
Kid: No [but looking a little afraid].
Me: They put metal wires in your mouth and glue brackets on your teeth and then pull it really tight with a wire and it’s really owie. Do you want to see what braces look like?
Kid: Yes…? [looking very anxious now]

I took them downstairs to the computer and using the ever-omniscient Google, I found this website. Check out Case #4 — it’s the most graphic [insert maniacal laugh]. I showed my kids these photos and they were 1) scared, because growing up in Southern California, they’ve never seen teeth this screwed up, and 2) they shrieked, “I don’t want to be like that!” and immediately gave up their habits.

There you have it. Tried and true.