EP 1001 - Lard of the Dance

From The Simpsons - Wiki on Neoseeker

When an intelligent girl named Alex comes to Springfield, she manages to get on Principal Skinner's good side and persuades him to allow her to organise a school dance. Lisa is overshadowed by the new girl and cannot find a date for the school dance. Depressed and slightly annoyed, Lisa sells tickets for the dance instead of attending the event. Meanwhile, Homer & Bart come up with a new get-rich-quick scheme - rounding up as much grease as they can and then selling it to a rendering plant. However when they try to take Springfield Elimentary's grease, Groundskeeper Willie is quick to react and attempts to stop them stealing the school's supply of grease. The air ducts fill with the stove's contents and grease falls from the ceiling. The children enjoy this, and play in the grease leaving Alex angry at their lack of sophistication. Once Lisa throws a grease-ball at her though, everyone acts their age, laughing and fighting in the grease.