<P> The theme song was co-written by Stu Gardner, Bill Cosby, and Dawnn Lewis--who was also a cast member . In the online interviews related to the 2006 "Hillman College Reunion," Lewis revealed that her being approached to write the song and to audition were two separate events that occurred within a short time of each other, such that she thought it was a practical joke by her friends . The song was performed by Phoebe Snow in season one, then by Aretha Franklin in seasons two through five, and Boyz II Men in season six . </P> <P> The spin - off program featured many appearances by characters from the parent program, especially in the initial season, in which Denise's father Cliff (Bill Cosby), mother Clair (Phylicia Rashad), younger sisters Vanessa (Tempestt Bledsoe) and Rudy, brother Theo (Malcolm - Jamal Warner), and grandfather Russell (Earle Hyman) all appeared on the show, either at Hillman or at the other end of a phone call . Denise's departure from Hillman after Season 1 did not stop her mother from reappearing on the show . Three of Phylicia Rashad's four appearances as Hillman alumna Clair Huxtable took place after season one, and in one of these, she brought her younger daughter Vanessa to tour the college . Sondra was the only Huxtable child not to appear on the show . Martin (Joseph C. Phillips) and Olivia (Raven Symone) appear in season 3 episode "Forever Hold Your Peace" along with Phylicia Rashad and Lisa Bonet . Elvin (Geoffrey Owens) and Pam (Erika Alexander) also never appeared on the show . </P> <P> Producer / director Debbie Allen is the real - life sister of Phylicia Rashad . Allen made one guest appearance on The Cosby Show, playing an aggressive aerobics instructor who helps Clair slim down for a special occasion . Allen appeared in later seasons in a recurring role as Whitley's psychiatrist . Dwayne and Whitley also visited the Huxtable home in an episode featuring the revelation that Denise had married and would not return to Hillman . </P> <P> A young Kadeem Hardison appeared on The Cosby Show as one of Theo Huxtable's friends in the first - season episode "A Shirt Story", though not playing Dwayne . </P>

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