The episode of the Simpsons in which Lisa takes ballet is “Lisa’s Sax”. This episode first aired in the United States on October 11th, 1990 and is the third episode of the second season.
In this episode, Lisa is desperate to learn how to play an instrument and Marge takes her to a music shop where she finds a saxophone that she loves. However, it’s too expensive for her family to purchase so Marge takes out a loan from Mr. Burns and Lisa begins to take lessons from Mrs. Krabappel.
Meanwhile, Bart takes up ballet as an extracurricular activity at school and soon becomes quite good at it. When he shows off his skills in front of his family, Lisa gets jealous and decides that she also wants to take ballet lessons. She begins taking classes with Mrs. Krabappel’s help and soon becomes quite proficient at it too.
At the end of the episode, Lisa and Bart perform a duet together with their respective instruments – Bart on his saxophone and Lisa on her pointe shoes – much to the delight of their family members present in the audience.
Conclusion:
The third episode of season two of The Simpsons entitled “Lisa’s Sax” is the one in which Lisa takes up ballet lessons after witnessing her brother Bart’s prowess at it. She eventually learns how to do pointe work sufficiently enough to perform a duet with him at the end of the episode, much to everyone’s delight.