I feel like this was heavily foreshadowed - the assertions from the ex teacher about Class 2-C not changing, the clear lack of heiarchy amongst the delinquents, etc. They are the same psychotic bullies from chapter one, except instead of Ogino being the target, their disorganized violence is now directed at whoever is deemed an enemy of Ogino.
I'm glad she's not being abused but the unpredictable and uncontrollable nature of these kids is going to collapse the house of cards, and soon