My school dreams have slightly shifted in style over the years, too, but definitely not in the same way like yours. For many years they were the classical „oh snap today we have exams/deadline of assignments/… and I’m not the least bit prepared“ but „wait a second I already graduated, I can care a little less maybe“. Now they are mostly in the vein of „I have already been to school and so I know I can do well here“. They are very confident now, I’m treading on very familiar ground. I still forgot homework every now and then or am completely unprepared but I’m full of improvisation in those situations.
As for the dreamscape and DCs, both are not very prominent in my school dreams. In many of them I don’t even enter school. For example I’m still at home packing my school bag. If I’m at school then it’s usually very focused on my desk. Teachers are mostly faceless DCs. In the past I dreamt about specific pastime teachers very often but now not so much anymore. As for school mates, usually there are only 1 or 2 that play a role in the dream, if at all. Those are almost always drawn from the pool of my closest friends back in school.
Reflecting on these changes as I’m writing this, I think a possible explanation for the evolution of both my dreams and also your dreams could be that memory of school times is slowly fading into the background so there are less details from your actual time at school that your brain can draw from. In your case this manifests in a more desolate dreamscape maybe. But the theme itself doesn’t get old in the same way because time in school was the most moulding experience in your life (I made a post about it a while back here, the whole thread is readworthy maybe).