Eu acredito que é Chance Fortune e os Outlaws por Shane Berryhill. O enredo de Goodreads parece combinar muito bem:
For as long as he can remember, fourteen-year-old Joshua Blevins has wanted to be a superhero. He has the brains, the passion, and the heart. There's only one problem: he doesn't have any superpowers. But Josh isn't about to let that stop him. Determined not to give up on his dream, Josh enlists the aid of his mentor, Captain Fearless, a retired costumed adventurer, to gain entrance to the Burlington Academy for the Superhuman under the false identity of Chance Fortune--a superhuman with the power of having unnaturally good luck. [...]
Além disso, se você estiver interessado, encontrei a resposta na página da Web em cache deste Pergunta do Reddit (na versão ao vivo, a resposta é deletada).