Dave Munger at Cognitive Daily takes a look at the "Mozart effect," the belief, that listening to Mozart can enhance testing ability, which has become the basis for an entire cottage industry aimed at the parents of young children.
The original Mozart observation was that adults performed better on a specific spatial test after listening to Mozart compared to a group exposed to relaxation stimuli. The idea that a particular music would improve test scores erupted into a "Mozart makes you smarter" frenzy. Mozart also improves your smile, removes ugly blemishes and increases your goats' milk production. You get the idea.
Regardless of the pop culture phenomena, the original observations were pretty interesting. Dave discusses to two efforts to replicate them which came to opposite conclusions. It might be that the reported difference lies instead in the exact sort of relaxation of the control group. Experiments using verbal cues to relax result in the Mozart effect, whereas listening to relaxing music (Debussy) erased the effect.
So: avoid telling your kids to relax. Otherwise they'll go dumb, and your goats will dry up.