Conversation so far:
What was Judy Garland's role in The Wizard of Oz?
Judy Garland played the main protagonist, Dorothy.
Did Judy Garland sing any songs?
Judy Garland sang the song with which she would afterward be constantly identified, Over the Rainbow.
What was The Wizard of Oz based on?
The Wizard of Oz was based on the 1900 children's book by L. Frank Baum.
How long did it take to complete the Wizard of Oz?
Shooting commenced on October 13, 1938, and The Wizard of Oz was completed on March 16, 1939.
Was the Wizard of Oz successful?
The Wizard of Oz was a tremendous critical success, though the film did not return a profit until it was rereleased in the 1940s and on subsequent occasions.
Did Judy Garland win any awards?
At the 1939 Academy Awards ceremony, Garland received her only Academy Award, an Academy Juvenile Award for her performances in 1939, including The Wizard of Oz and Babes in Arms.

Question: What was the award for?
Self-contained rewrite: What was the Judy Garland's Academy Award for?