Hi,
I see that you've only watched Korean dramas so far so I'll give you suggestions for both. I reckon you should try watching Chinese school dramas because they honestly do it the best out of all of them. I used to watch a lot of Korean ones but now all I watch are the chinese ones because their SO GOOD!
KOREAN:
To The Beautiful You- some may disagree but I absolutely loved this. If you enjoy this then you should try watching the Japanese version as well, really good.
The Reply Series (1997, 1994, 1988)- This series is such a gem, I personally really enjoyed it with my fav being the 1988 version.
Weightlifting Fairy Kim Bok Joo- Another absolute gem, not entirely a school drama as it focuses more on the sports side but still goes through their collage life.
School 2017- Got a bit sidetracked at the end but still pretty good and had the mystery aspect to it as well.
Go Back Couple- A time travel/school drama. Such a good drama and made me cry a lot, definitely give this a try.
Girls Generation 1979- Gives you the Reply series vibes and really good at the same time. I wish it was longer but it ended up being a pretty short drama.
CHINESE:
Where the Lost Ones Go- My absolute favourite of all time. A very underrated gem that I wish everyone would watch so give this a try.
A Love So Beautiful- Really good as well, doesn't have too many obstacles that get in the way of the main couple which I honestly need sometimes in a drama.
Unrequited Love- Very very good as well, this one is pretty recent so it just finished airing.
Le Coup de Foudre- Another really good gem, the OST in this is so very well done and fits the drama perfectly.
My Sunshine- An older one but one I just can't seem to forget and honestly one of my all time favorites.
Just an Encore- This one is pretty recent as well and quite good.
Wait, My Youth- Also recent and really good.
When we Were Young- I actually still haven't finished this one but it was quite popular and from what I've seen really good as well.
With You- Tried to watch this but never really got past the first couple of episodes but it is highly rated so I probably will try to watch it again soon.
My Huckleberry Friends- This one is linked to With You and also quite popular, still haven't personally seen this though.
Somewhere Only We Know- Really cute drama, also pretty recent.
JAPAENSE-
Hana Yori Dango- The Japanese version of Boys Over Flowers (if you've seen it) and my most favourite version as well. If you like this then I reckon you should give the other versions a try as well but this still is my personal favourite.
Hana Kimi- The Japanese version of To The Beautiful You, I sorta liked this a bit more than the korean version but their both really good.
To be honest, my suggestions could go on forever but you can also search MDL for school dramas by narrowing down your search. Also, try other genres of dramas as there are some really good ones that are not school dramas.
Hope this helps :)