Hercules and the First Day of School

Hercules and the First Day of School is an episode of Hercules: The Animated Series. Though chronologically the first episode, it would be the 11th aired, premiering on September 21, 1998

Summary
When the narrator starts to tell a story of Hercules' adventures, the Muses interrupt him by informing him of his greatest challenge: high school. Skeptical, the Muses then proceed to tell the story of how Hercules began his education at Prometheus Academy. Beginning at Phil's Island, Hermes drops on by to wish Hercules luck and remind him to catch the ferry to school, though it ends up breaking during Hercules' rushing jump to board. Already looked down on, Hercules soon befriends Icarus and Cassandra and ends up being humilated by Adonis, who deems Herc to be a worthless nobody. Wanting to prove himself to the student body, Hercules goes after the two headed cyclops Orthos. Orthos has been told by his mother Echidna to start eating more important people and when meeting Hercules and deeming him not worthy of the effort, they do decide to go attack Prometheus Academy and it's most important students. Hercules ends up saving the school from the monster, though Adonis ends up stealing the credit. Hercules doesn't mind and just chooses to accept it and himself.