Girls’ Dormitory (1936)
Marie Claudel (Simone Simon) falls in love with her school principal, Dr Stephen Dominick (Herbert Marshall).

Margie (1946)
Margie (Jeanne Crain) falls in love with her high school French teacher, Professor Ralph Fontayne (Glenn Langan).

The Romantic Age/Naughty Arlette (1949)
Arlette (Mai Zetterling) seduces her middle-aged art master, Arnold Dickson (Hugh Williams).

Noce Blanche (1989)
Mathilde Tessier (Vanessa Paradis) has an affair with her philosophy teacher, François Hainaut (Bruno Cremer).

For My Daughter’s Honor/Indecent Seduction (1996)
Amy Dustin (Nicholle Tom) has an affair with the school biology teacher and football coach, Pete Nash (Gary Cole).

Carried Away/Acts of Love (1996)
Rosealee Henson (Amy Locane) seduces her schoolteacher, Joseph Svenden (Dennis Hopper).

Blue Car (2002)
Megan Denning (Agnes Bruckner) has an affair with her English teacher, Auster (David Straithairn).

La Belle Personne/The Beautiful Person (2008)
Junie (Léa Seydoux) is pursued by her Italian teacher Nemours (Louis Garrel).

Daydream Nation (2010)
Caroline Wexler (Kat Dennings) has a fling with her English teacher Barry Anderson (Josh Lucas).

Palo Alto (2013)
April (Emma Roberts) has a liaison with her school football coach, Mr B (James Franco).

Breathe In (2013)
Sophie (Felicity Jones) falls in love with her married music teacher, Keith Reynolds (Guy Pearce).

Molly Maxwell (2015)
Molly (Lola Tash) has a forbidden relationship with her English teacher, Ben Carter (Charlie Carrick).

Reader Omlil also suggests the following Japanese films:

Koukou Kyoushi (1993)
Tenshi no Koi/My Rainy Days (2009)
Kinkyori Renai/Close Range Love (2014)
Sensei!/My Teacher (2017)