Mirette on the High Wire by Emily Arold McCully

From chapters.ca:
Mirette was always fascinated by the strange and interesting people who stayed in her mother's boarding house. But no one excited her as much as Bellini, who walks the clothesline with the grace and ease of a bird. When Mirette discovers that fear has kept him from performing for years, she sets out to show him that sometimes a student can be the greatest teacher of all.