The show's title comes from a classic school prank where a victim is tricked into writing 'PEN15' on their hand after being invited to join the 'Pen 15 Club,' since the word resembles 'penis.'

The series is based on the childhood experiences of creators Maya Erskine and Anna Konkle, even though in real life the two didn't actually meet until college.

Erskine and Konkle, both 31 at the start of the show, play 13-year-old versions of themselves surrounded by real teenage actors.

The creators originally wanted other teenage characters to also be played by adult actors, but decided Maya and Anna would be the only ones, since it made them feel more like outsiders or 'aliens' among the real kids.

During sexual scenes, the underage actors were replaced with adult stunt doubles.

Filming of the second season was severely delayed by the COVID-19 pandemic; the show was originally intended to run for three seasons, but by the time season two wrapped, both Erskine and Konkle had taken on new acting roles and parental responsibilities, contributing to the decision to end the series after season two.

To recreate the early-2000s setting, production designer Grace Alie and set decorator Ali Rubinfeld drew on their own and their siblings' childhood bedrooms, old magazines from a downtown Los Angeles library, and shows like Are You Afraid of the Dark? and Lizzie McGuire; many props were sourced from thrift stores in Los Angeles and Palm Springs or bought on eBay, including vintage Teen Beat magazines and a Unisonic phone.

Budget constraints were the biggest challenge during season one, forcing the team to be resourceful with spending and location scouting, while season two had a larger budget allowing them to build elaborate sets on stage; whiteboards in the middle school were even replaced with chalkboards to fit the era.