While this isn't explicitly stated in the book, it is implied in *Harry Potter and the Half-Blood Prince*. J.K. Rowling confirmed this detail in an interview:
> "Draco Malfoy dances with Astoria Greengrass at the Yule Ball," she told Scholastic. "She is a very nice witch, and she is in Slytherin. Astoria is a pure-blood witch, and she doesn't subscribe to Draco's nasty prejudices. She loves him anyway, and she eventually helps him see that there is more to life than just being a Death Eater."
While this is a detail revealed after the events of *Harry Potter and the Goblet of Fire*, it clarifies who Draco dances with at the Yule Ball.