You know that you're not happy at school. By knowing how the character especially the protagonist speaks, you can create consistency whenever the character dialogues with others.
Good dialogue evokes the way people actually talk in real life without actually sounding precisely like the way people talk in real life Paraphrasing Elmore Leonardgood writers leave out the boring parts. The only exception to this rule is when a character makes a long speech.
You want to make sure when writing that every word your characters say has a clear reason for being said. I looked away from the mirror, at her. Info dump is a large amount of exposition given all at once, and left for the reader to sort out.
However, the rules remain the same for any type of dialogue be it a short story, full novel or any kind of dialogue.
Lengthy dialogue can be exhausting for the reader. Dialogue is a useful tool for developing your characters and moving your plot forward.