It totally makes sense that since this is a first-person narrative, we learn a lot about Sasha from what goes on inside his head. One of the first things we learn from his thoughts and attitudes toward others is that he's naive. He thinks Stalin is a "brilliant genius of humanity" (13.4) (when he's actually a cruel and brutal dictator). We're also hip to the fact that he thinks the best of people, even when that proves to be a bad move: his dad is the greatest hero of all Communism (1.1), and Nina Petrovna is the bestest teacher who ever chalked her name on a blackboard (13.11). A clue: Both of these turn out to be not-so-true.
From Nina Petrovna engaging in brutal fisticuffs with her own student, to the Senior Lieutenant of the State Security stepping up to arrest children for being terrorists, actions go a long way in this book toward giving us the skinny on Yelchin's characters.
For example, we can easily figure out that the Senior Lieutenant is a ruthless and cold enforcer of the State because he's willing to knock people around, arrest them in the middle of the night, and coerce children into becoming spies by hanging the threat of prison over their heads. On the other hand, we know Sasha even early on rejects many of the things he's been taught: he initially refuses to throw the snowball at Four-Eyes, later feels sorry about it and refuses to laugh at him (when all of the other children do so), and risks his own life to wait in the freezing cold (behind roughly eleventy-hundred people) to try to visit his dad in prison.
Words, words, words. In Breaking Stalin's Nose, we can tell a lot about people by how they speak to others. Nina Petrovna and Sergei Ivanych don't shy away from throwing around racial slurs: she makes fun of Four-Eyes for rocking back and forth, taunting him that he's "not in synagogue" (13.19); and the principal sneeringly notes that he's gotten rid of "that Jew, Finkelstein" (23.18). There are some silver linings to these clouds, though, and through speech and dialogue, we get a few examples of characters who are kind: Sasha (of course!) and the nice lady in line at Lubyanka prison.