This is based on opinion. Please don't list it on a work's trope example list.
Tear Jerker / Freedom Writers
Many, if not all, of the students that Erin teaches have extremely sad Back Stories, mostly about family members being sent to jail, beaten, or even killed, as well as friends.
While the entire movie kind of gently tugs at your heartstrings, the biggest bit is the "Toast for Change" scene. One student reads an entry from his journal, which recounts the time when he and his mom got evicted from their house, and how worried he was about being made fun of for being homeless. But when he came to his English class' first hour, nothing else mattered. He was home. He reads it all on the verge of tears himself, and then the whole class—people who were formerly gang rivals who hated one another—gather around him for a group hug.
Erin Gruwell's divorce. Considering she spent so much time wanting to help her students that she spent away from her husband, so much so he spends his time complaining before finally deciding to leave her. It's heartbreaking especially considering how much Erin spends most of the film in smiles despite everything that occurs.