[@McHaggis] Alright, how about the [I]family[/I] being recently rich types with sandbender in the blood (the character's grandparents) they've sworn off to fit in with Middle Ring Ba Sing Se culture. The character is a bender, but is incredibly poor at earthbending (which the parents would encourage) but is naturally talented at sandbending.

The character attends an earthbending academy, and has to often stay for extra lessons (aka cleaning up, a punishment from a bad teacher). The character learns/practices their talent with the dust and powder left over from the training rocks/discs. The parents are embarrassed by this talent, despite the fact it makes the character the equal or better of their peers.

As for the airbending teacher, I'd be interested in exploring cross-cultural influences; the loose, shifting nature of sand might make air- or waterbending techniques applicable in the same way waterbending was applicable to lightningbending. The character would be thoroughly outclassed by a real sandbender, but the other bending styles would teach them tricks and skills a "pure" sandbender might not know.