We think the theme in this story is, if you make trustworthy friends they can teach / help you and you can do the same to them. We think this because Matt teaches Attean English and Attean taught Matt survival tips and tricks.
The craft technique that the author used was dialogue. She added dialogue to show communication between characters. For example, the readers would not know that Attean call Matt brother at the end.
Sign Of The Beaver,by Elizabeth Spear. The main problem in the story is that Matt has to survive in the wild alone with no gun because his dad had to leave to get the rest of the family and Ben stole his gun.