John as illustrated by Adam McCauley (left) and as he appears in the cartoon (right)
| Hair color:
|| Light brown (books)
| Eye color:
|| fools human
|| February 8,
|| Thanks guys, but it's no use. I'm just one upside-down failure!
— John in "Upside Down John"
John is a student in Mrs. Jewls' class on the 30th floor who is always upside down. According to Mrs. Jewls, his ancestors created fire, underwear, and the exploding test tube thanks to being upside down, and they have all helped humankind (although the exploding test tube is debateable). In the books, only his brain was flipped upside-down, and he could never stand on his head, but the TV show shows him being upside-down altogether. He is also mentioned to be one of the smartest students in class.
John is a student with a round head. In the books, he has short, light brown hair, but in the cartoon, he has medium-length dark blue hair. His skin is a tan color. He has a large nose and somewhat small eyes. He wears a creme-coloured shirt and magenta-colored vest. His pants are a tealish-blue. He has dark teal sneakers with a white sole and laces. In the cartoon, he is always standing on his head.
- Due to his Upside-Down nature, John is also reffered to as Upside-Down John.
- In the pilot, John is voiced by Dwayne Hill (who voiced Papa Jewls, Mrs. Jewls' father), in the show, he is voiced by Megan Fahlenbock (the actress who also voices Gwen on TDI/TDA/TDM/ and Jen Masterson on 6teen)
- John has a family that are also upside down.
- Since he is most often in his desk in the cartoon, anything aside from his legs are rarely seen.