The original study found a brief spatial-task bump, not a lasting IQ gain; meta-analysis shows the effect is tiny and probably just arousal.
What the evidence shows
The 1993 Nature study reported that college students who listened to ten minutes of Mozart did slightly better on a spatial-reasoning task than students who sat in silence. The finding was narrow and temporary — it lasted about fifteen minutes and concerned one type of task — but the press turned it into 'Mozart makes babies smarter,' and some US states even distributed classical CDs to newborns.
A large meta-analysis by Pietschnig, Voracek & Formann (2010), pooling nearly 40 studies and over 3,000 participants, found the effect was very small and largely disappeared in independent labs. The best explanation is 'arousal and mood': any enjoyable, stimulating input can nudge short-term performance, whether it is Mozart, a Stephen King audiobook, or an upbeat pop song. There is no evidence that listening to Mozart raises general intelligence.
Sources
Rauscher, F. H., Shaw, G. L., & Ky, K. N. (1993). Music and spatial task performance.
Nature, 365(6447), 611
Students briefly performed better on a spatial task after listening to Mozart than after silence — an effect lasting only minutes.
DOI: 10.1038/365611a0 →Pietschnig, J., Voracek, M., & Formann, A. K. (2010). Mozart effect–Shmozart effect: A meta-analysis.
Intelligence, 38(3), 314–323
Across ~40 studies the effect was very small and mostly absent outside the original lab, consistent with a mood/arousal explanation rather than raised intelligence.
DOI: 10.1016/j.intell.2010.03.001 →