DS1 has been thumb-sucking forever. He's almost five. He sucks his thumb throughout the day. His new school are not too keen on it, and suggested a solution - he wears a plaster on the appropriate thumb.
We just started today, and he seems pretty happy with it. It certainly helps that he wants to stop sucking his thumb, and he's happy to wear the plasters (batman ones). We've agreed he won't have to wear them to bed, as I don't think nighttime thumb sucking is that bad, and anyway, one battle at a time ...