Arbitrary?

One of my nieces started kindergarten this fall, and I asked her father what she thinks of school.

"She likes the bus. She's fascinated by the bus," he said. "But she can't figure out why these kids still need to learn their ABCs and 123s. She had those mastered a long time ago. She says school is boring." Then a twinkle came to his eye. "And I believe she used the word arbitrary."