Why didn't my rufflet learn superpower at lvl 51 (pokemon white)?

Question

HELP!!! my rufflet didn't learn superpower at lvl 51. it was at lvl 49 when I fed it rare candies to evolve it to lvl51. I scratched the move skydrop when my rufflet tried to learn it at lvl 50. it's now a braviary and at lvl 55 but the move superpower hasn't popped up. :((

Answer 1

That's because Rufflet doesn't learn Superpower via Level Up. It only gets it from the Black & White 2 Move Tutors. You must have a Braviary level up to 51 to get Superpower. To get it now, get a Heart Scale (Driftveil City, there's a woman that will give you one for showing her a move), and bring it to Mistralton City and go to the move relearner to get Superpower.

Source (Rufflet)
Source (Braviary)

Answer 2

Rufflet doesn't get Superpower and doesn't evolve into Braviary until level 54. Braviary, however learns it at level 51, but to get Braviary to learn it you need to take it to the Move Relearner in Mistralton City and teach it in exchange for a Heart Scale.

Sources: Rufflet / Braviary