Well, I can't really object to the extremes theory. You aren't a Third-Worlder or a highly driven Indian or Chinese or pre-20th century American child who wouldn't be bothered by such conditions, after all.

But most school building is not about avoiding such extremes. I can cite exactly one example in my educational career where a building had a massive overhaul due to genuine need (a fire in the gym burned the roof badly); all the other expansions and new buildings.... not so much.

Its very difficult to keep focused when the classroom is 30 degrees Celcius and the lecture is two hours long.

This reflects a failure of pedagogy more than the value of architecture - I've never seen any research saying students can really focus & learn for 2 hours, and the research I glanced over suggest much shorter lectures than that. (IIRC, the FAA or USAF found pilot-education lectures should be no longer than 20 minutes and followed immediately by review.)