 Balliett used art and blank plates as inspiration for the characters ' names . Calder Pillay is derived from the artist Alexander Calder and Petra Andalee was inspired by the architecture in Petra , Jordan . The names were meant to be different , which Balliett considered " fun for a child . " Balliett felt that she could capture the attention of reluctant readers if they related to characters who enjoyed writing and math . Calder and Petra 's teacher , Ms. Hussey , was inspired by an old name on Nantucket Island and the old @-@ fashioned word <unk> . Balliett compares herself to Ms. Hussey , stating that " [ we ] think a lot alike . " Some of Ms. Hussey 's assignments and dialogue even came from Balliett 's classroom . She chose the setting of Hyde Park , Chicago , where she currently lives , because she considered it full of secrets that children could discover . 
