The 'Mozart effect' phenomenon was first suggested by a scientific study published in 1993 in the respected journal Science.
It showed that teenagers who listened to Mozart's 1781 Sonata for Two Pianos in D major performed better in reasoning tests than adolescents who listened to something else or who had been in a silent room. The study (which did not look at the effect of Mozart on babies) found that college students who listened to a Mozart sonata for a few minutes before taking a test that measured spatial relationship skills did better than students who took the test after listening to another musician or no music at all.
The finding, by a group at the University of California whose study involved only 36 students, led crèches in America to start playing classical music to children and the southern US state of Georgia even gave newborns a free classical CD. Most recently Helena Bonham Carter has said that listening to Mozart and other classical music while pregnant has made my children 'unbelievably smart'. But there has been debate since about whether the effect exists.