Pixar's Trolls meets Jeanne DuPrau's City of Ember meets Tolkein's Lord of the Rings

Bbor, a clumsy dwarf of thirteen, isn't smart or destined for anything great. In fact, all he seems to be good for is working in the mines. The world he lives in is ruled by intelligent and magically-proficient gnomes while dwarves, a minority race, are forced into unpleasant, labor-intensive positions.
Bbor envisions another future for himself, however, and he is determined to make himself smart and enter the famous Lyceum, a magical institute almost exclusively for gnomes. He steals books and reads in secret to train his mind but must also deal with the stress of the mines and bullies within, the loss of his best friend, and eventually becoming a social outcast.
When dreaded wraiths, immune to magic and arrows, threaten the entire realm and all hope seems lost, the seemingly-unusual things that Bbor picked up from reading his stolen books may be the only way to save everyone... but will anyone listen to a teenage dwarf in time for him to make a difference?