I do the mix-up-the-horoscopes-and-see-if-they-can-correctly-identify-their-own game with my 6 through 8th grade science club every year. Of course they can't get it right at a rate above random chance, but when the game is over, they read their "real" one and invariably, many say something like "Oh yeah, this fits much better". Just got through showing what hooey it is, and they draw the bulls-eye around the dart anyhow. Powerful stuff this belief.

Now, about dowsing...