What episode did Leonardo di Caprio first appear on Growing Pains as Luke?

Leonardo DiCaprio was invited to join the cast of the hit ABC sitcom, "Growing Pains" playing the role of Luke, a troubled homeless boy taken in by the Seavers.
The first time he appeared on the show was in the episode: "Back to School" (sept 18 1991).
He appeared on 23 episodes.

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