
OMG! There are so many to pick from. Its like 1/3 of all the yaoi manga.
These are 2 of my faves.
http://www.mangago.zone/read-manga/adam_no_junjou/
http://www.mangago.zone/read-manga/bokura_no_unsei/
But there are 39 pages of anything highschool related.
http://www.mangago.zone/r/l_search/?page=1&name=high+school+yaoi

I love this one its cute with good plot
http://www.mangago.zone/read-manga/count/

http://www.mangago.zone/read-manga/kono_ore_ga_omae_nanka_suki_na_wakenai/
http://www.mangago.zone/read-manga/rutta_to_kodama/
http://www.mangago.zone/read-manga/hatsuai/
http://www.mangago.zone/read-manga/dounimo_nannai_soushi_souai/
http://www.mangago.zone/read-manga/i_want_to_be_naughty/ (the first two couples from the warui series)
http://www.mangago.zone/read-manga/hanayome_kun/
http://www.mangago.zone/read-manga/karada_meate_de_warui_ka/
http://www.mangago.zone/read-manga/elektel_delusion/
http://www.mangago.zone/read-manga/koi_nante_shinai/
http://www.mangago.zone/read-manga/megane_goshi_no_sora_wa/
http://www.mangago.zone/read-manga/twinkle/
http://www.mangago.zone/read-manga/dash/

Read the Warui series. It's really good. Here is the list in order.
1. Warui Koto Shitai
2. Warui Ko Demo Ii?
3. Kirai ja Nai Kedo
4. Warui Yatsu Demo Ii
5. Koi ja Nai Kedo
- Warui Koto Bakkashite Gomennasai
6. Mujihi na Otoko
7. Warui Koibito ja Dame?
8. Kare ja Nai Kedo
9. Mujihi na Anata
10. Sunao ja Nai Kedo
11. Warui Ouji Demo Suki
12. Mujihi na Karada
- Seiaku Ookami ga Koi o Shitarashii
sweet highschool yaois?