S14E03 Bart vs. Lisa vs. 3rd Grade
When Bart is held back a year and Lisa fast-streamed they end up in the same class where, for once, Bart is the star pupil because he has already learned the material. Things worsen between them on a field trip where they are called upon to design a new flag for the state of Springfield and Bart sabotages his sister's efforts. After they fight they get lost in the woods before they are found by a hill-billy family and returned home. After this Principal Skinner feels it best to return them to their old classes.