Gonna copy Sephiroth's idea [ Hope that this is alright ]
Biology: Going to choose Dr Gast for this one
Languages: Rikku, being Al Bhed and everything. Sometimes a little too silly, and doesn't give out enough homework, though she's still adored and respected.
Law: Cyan, very serious and old fashioned, sometimes because the jokes of the students since he's easy to get emotional, but by the end of every year, he always wins his students over. During reunions, past students always come back saying that he was their fav teacher.
Philosophy/Literature: Genesis, each year, each student has to study his favorite book Loveless.
Music: Julia Heartilly, due to her piano skills and her writing that famous love song Eyes On Me
Chemistry: Kefka, he's a little more sane, though sometimes he gets carried away, most of his students believe that he would totally use his chemistry skills to do something completely nasty.
Geography: Aerith, since she basically knows about the world and everything around it.
Art: FF VI Relm, because there's nobody else ?
Religious education: Yuna, Wakka would be more into teaching sport and don't really see Lulu as a teacher. Very kind, very understanding, and even to students who don't believe in Yevon.
Math: Sephiroth, can picture him wearing those nerdy glasses too. Cannot stand the literature teacher.
History: Ashe, she would be very serious about it too, and if you fool around her in class, she'll kick you out, and you'll never be allowed to return, unless you make a very serious genuine apology.
Psychology: Quistis Trepe, can see her doing this, and being good at it, until she falls in love with her student Squall, and fails to understand him, and then second questioning her work, knowledge and skills.
Drama and theater : Kuja, duh. Still narcissistic, though he's extra soft on his younger brother Zidane. Just like Ashe, if you don't take his classes seriously, you're gone. If you fail or slip up, he's extra harsh on you, believing that you're being a insult to the arts.
Physical Education : Wakka would make a terrible teacher since he can't win a single game, so going to say Zack Fair. Most girls take his classes, because they're in love with the teacher. Mr Fair doesn't mind at all.
Cecil- Starts off as the troubled students who fails all his classes, but then turns around, and starts getting A+ scores, and loved by the teachers. Best at religious studies.
Kain- Starts off as a A+ student and only friend to Cecil but when Rosa and Cecil start dating, and becoming a couple, Kain snaps and ends up leaving school, becoming a dropout.
Terra- Shy, misfit and usually bullied by harsher students, has a huge fear of the chemistry teacher Kefka, until she starts making more and more friends, and then she no longer fears him.
Cloud- Wants to be popular and cool, like Kain and the PE teacher Mr Fair, but he can't. By the second half of the year, he ends up befriending the teacher, and becomes more cool. Cloud has a crush on the geography teacher Aerith, but ends up finding out that she's dating his role model.
Squall- That anti- social student, that doesn't say a word usually. Best at Psychology class. However he soon to begin to date the daughter of the music teacher, and becomes a different student, much more brighter, and ends up making alot of friends.
Seifer- Squall's only friend, however he's lost within his own fantasy world. Best at literature class, and Genesis loves his creative writing stories. However Rinoa dumps him, worried that his fantasy dreams were making him a little creepy. Begins to hate and loathe Squall.
Zidane- Complete playboy, and pretty chill, and usually doesn't do his homework unless it's his older brothers class; seems to be the only one who can get on Kuja's good side. Starts off as arrogrant, but then becomes the one who starts befriending and standing up for the misfits.
Princess Garnet- Awarded most beautiful girl at school, and is nicknamed princess because of it. She's worried about her mentally unwell adoptive Mother, and her studies, and would prefer to care less what a bunch of teens think of her. Ends up in a relationship with Zidane.
Tidus- Student from a different country and different school, and befriends the religious studies teacher Yuna, and ends up falling in love with her, however they can't, making their love forbidden.
Hope- Used to be a happier and confident student, until his mother passed away, now he yells, shouts and becomes completely emotional. Becomes friends with Claire Farron. Usually doesn't do his homework, and the teachers ( expect Sephiroth, Genesis, Kefka and Kuja ) understand. Thanks to Claire and other friends, becomes a stronger person and starts getting better scores on tests.