Symbolism, Imagery, Allegory
Here's our first glimpse of a Stalin statue (and you can also take a peek at the drawing at 5.F1):
[A] giant statue of Stalin gleams under searchlights. The statue is made from the steel of fighter planes and stands taller than any building. You can see it from every window in Moscow. (5.3)
This statue is tall, powerful and strong. Plus it's made out of war materials, so you know it's tough. It is also surrounded by "searchlights" and you can bet that if it can be seen from every window in Moscow, it can look right back into those windows. Big Brother truly is watching these folks. So what's the ultimate impression we get from this imagery? All-powerfulness.
The plaster statue at school (after which the novel is titled) is rather puny in comparison. No doubt it's a miniature version of the big statue, meant to mean the same things to the kids at school: Stalin is powerful, strong, and watching you.
But unlike the tall statue, this one has weaknesses. The fact that its nose can be broken off suggests that in some ways, Stalin's power can be chipped away, even if it's just a little bit at a time.