Fitzhugh wrote two sequels, The Long Secret (1965) and Sport (1979), which maintain the gay symbolism. But in the 2000s, sequels by two other authors heterosexualize Sport. Harriet Spies Again (2002) by Helen Ericson, gives Sport a crush on a girl. And Harriet the Spy, Double Agent (2005), by Maya Gold, involves Sport and Harriet competing over the same girl.
One wonders why they heterosexualized Sport but not Harriet. Maybe there is more cultural anxiety about gay boys than gay girls.
There have been two film versions. Nickelodeon's Harriet the Spy (1996), starring Michelle Trachtenberg as Harriet and gay-friendly actor Gregory Smith as Sport, leaves the gay subtexts intact.
Director Bronwen Hughes has also directed episodes of The L-Word and produced the movie Woman on Top (2009), which features a gay "best friend," so she is not unaware of gay/lesbian characters. Plus, notable lesbian actress Rosie O'Donnell plays Harriet's nanny, Golly.
The Disney Channel's Harriet the Spy: Blog Wars (2010), starring Jennifer Stone, makes Harriet a teenager who has "modern" problems like "mean girls" and "hot boys." She is interested in a movie star, Skander (Wesley Morgan, who previously played a gay character on Degrassi High). When he comes to town to film Spy Teen 2: The Sequel, she stalks him and blogs about him so obsessively that her friends Janie and Sport dump her, and Skander quits the movie in disgust. But in the end she apologizes, and Skander gets a role in a new movie and hugs her.
There still is no heterosexual romance -- Harriet never "gets with" Skander (who doesn't seem interested in girls) -- and Sport remains neat, fussy, artistic, a gay-vague best friend. Even the crush that drives the plot seems less about Harriet's interest in the hot boy than her attempt to find an interesting topic to blog about. The heterosexualization is minimal, a nod to the modern censors who yell that kids must never, never become aware that gay people exist.