reading order for Doukyuusei -Classmates manga

doukyuusei (classmates) -> sotsugyousei (graduates) -> o.b. -> blanc

sora to hara and futari gurashi are both spinoff manga, sora to hara can be read anytime after doukyuusei and futari gurashi should be read after blanc

1. doukyuusei
2. sotsugyousei
3. sora to hara - story of teacher [spin-off]
4. O.B. - ocupation to beloved
5. dousoukai
6. blanc [epilogue]

hope this helps!