Lol, my first thoughts, they barricaded themselves in the school as a protest. In order to accomplish that, they would have had to wake up really early collectively, and arrive at the school before any teacher or staff member. They'd need to somehow enter the school then, and then spend an hour or so gathering all the furniture to create the barricade that covers the entrance. In all this time, no teacher or staff member has yet to arrive and stop them. 😂 Or maybe... they'd have a staff member who helped them with setting all this up, but still a lot of effort as opposed to simply boycotting the school? Or gathering at the school entrance and protesting to garner attention. Barricading themselves in the school is just stupid lol.
And I still don't understand what this second arc has to do in connection with the first one besides having MC now as a teacher, and some cameos from the previous antagonist. Also, how the hell is Mouri even more well informed about what is happening in that school than Imabari who's working there? Assuming she's directly involved in what's going on, then why is she trying to help Imabari? So many things that just don't add up.
Honestly this should have ended with the first part. They could have made this as a sequel separate from the first part. Not that that explains away a lot of the things that just aren't making any sense here.