On what basis can people be categorized?

A new teacher has arrived for the fourth grade!

She is also the school principal. She is Valeria Kirillovna, or "Valkyrie" for short. She is a witch. Not an evil one, mind you—just strict but fair. And one who uses advanced teaching methods...

Tell me, could ordinary teachers transport a lazy student into a calculator to show him why math is necessary? And is an average teacher capable of placing kids who were lost in the pages of "The Wizard of the Emerald City" on a riverbank, practically into the clutches of saber-toothed tigers? Or bringing a math textbook to life so that pedestrians and cyclists moving toward each other gain substance and become perfectly simple and understandable? Or conjuring a combination lock on the door, turning the classroom into an escape room that can only be exited by demonstrating collective ingenuity?

Yes, the lives of the fourth-graders are no longer dull, but it’s not all just spells—even without magic, the school is constantly in motion: holidays, contests, inter-class str̶u̶g̶g̶l̶e̶ competition, and intra-class relationships. Some fall in love, others quarrel, and some weave intrigues. Yet, work still needs to be done, so putting their likes and dislikes aside, the classmates work together toward common goals.

At first, it seems that this book is primarily entertaining, without complex themes, just an intertwining of school and fairy-tale events. But everything changes with the final adventure organized by the witch-teacher for her favorite class. Seeing the excessive fervor with which the children play the military game "Zarnitsa," Valkyrie transports them to a world where people are divided into "us" and "them" by... hair color. Blondes and brunettes have been implacable enemies since time immemorial, and redheads are outcasts altogether. And it gets quite frightening: political indoctrination, propaganda speeches, global conspiracies, dehumanization, vigilante justice, regulations, endless rules, hatred... What conclusion do the young travelers draw from what they’ve seen? The only right one: WE MUST NOT FIGHT FOR PEACE, WE MUST NOT WAGE WAR.