John P. Tristate Elementary is the school in which Phineas and Ferb attend.
The school has barely even been seen in the show, since the series takes place in the summer. However, it has made a few minor appearances. In "Are You My Mummy?", during the song "My Undead Mummy", a scene showed what would happen if Phineas and Ferb brought a mummy to school, and all the students watched in awe as Phineas and Ferb's mummy started DJing for them.
In "Doof 101", Phineas and Ferb were seen on their first day of school, modifying the playground to make it more awesome. Sally was seen calling out to them, wondering when they'd be done. Phineas and Ferb then looked over at Danville High School, and said that they were so excited to go to high school when they were older.