I don't really know what exactly to say about this drama. First of all, the easy stuff, realistic school life, they actually study. The hard stuff now, I don't know how easy someone can speak about these things like underage sex trafficking, and mental health issues. In a enviroment that can remind a Steven King story (young people, school as a small community etc), this drama speaks about that with realistic enough way. About the trauma and the reasons behind it. And how to some people the hardships of others is something far away and a "game".
That was the main point, but as the story went by I think it became a little too much complicated with this gang stuff. And I think it wasn't needed. The story as a whole had more potential, always I had a feeling that it was good but with something missing. The story and the end had some similarities with Parasite, someone with nothing using illegal methods to climb the social ladder and the way the story is solved. I think it is just a Korean dark thing the end. I have watched crime dark series and movies from differents countries and korean ones are some of the darkest.
Also, really great acting, especially Kim Dong Hee (I loved him from Itaewon Class but in Extracarricular he is amazing) and Choi Min Soo. And congratulations to Park Joo Hyun for creating a really annoying and completely fitting character as Bae Gyu Ri.

(English isn't my first language, sorry for any mistakes)