Answer: The pregnancy of one of its stars
Due to the pregnancy of Brenda, one of the show's Council Members, a spot opens up for a new member. Determined to seize this rare opportunity, Tracy skips school in order to audition, only to have her hopes dashed by the obnoxious Velma Von Tassle. For the vindictive Velma tells Tracy bluntly that her size is an issue, as is her support of integration, and so she is rejected, Later on in detention, which is Tracy's punishment for skipping school, she meets Seaweed, who performs on "The Corny Collins Show" on "Negro Day". He and his friends are all wonderful dancers, and soon enough Tracy is dancing alongside them, impressing them with her moves.