“All Brazilians know how to dance,” says the mother of one of the two ballet students at the heart of Only When I Dance. “It’s in our blood.” No one who has seen YouTube’s latest darling—a Brazilian baby working some serious samba moves—could disagree. Making a life of it, however—or several lives, in the case of poor dancers struggling to elevate their families—is another story. Irlan, a laser-focused and somewhat taciturn young man who comes alive onstage, is an obvious star. Even his father, who was initially mortified by his son’s passion, has given in (now it is Irlan who is mortified to see his name tattooed across his father’s forearm). Isabella, as the dance academy’s sketchy headmistress reminds us several times, is black. If she thought that made life tough in Brazil, the ballet world redefines discrimination. Her frustration with her body’s natural shape is heartbreaking; that she is encouraged to starve while her family lives on the edge of poverty is mind-boggling. British director Beadie Finzi follows both dancers to international competitions, where the difficult questions raised by their struggles are set aside. Success follows for one of them, but a pat ending leaves the feeling that these dancers didn’t get their due.