Azumanga Daioh
The series is centered on 27-year-old homeroom teacher Mika Suzuki (who only looks about half her age) and the eccentric and colorful students of her class. The anime, coming two years after J.C.Staff had success with "Azumanga Daioh", inherits a lot stylistically from that series, however the original manga predates "Azumanga Daioh" by two years. Additionally, before the recent anime incarnation, the manga spawned a series of drama CDs.