All image and audio content is used by permission of the copyright holders or their agents, and/or according to fair dealing as per the UK Copyright, Designs and Patents Act 1988. Nurse's Office" and " Orange Juice" are the only two songs on the album that are not considered explicit.

On September 25th, 2020, Melanie released her fourth EP “After School” alongside a deluxe version of K-12, which included the original tracklist and all songs from “After-School”. The album marked her first full-length studio album in four years since the release of 2015’s Cry Baby. Additionally, this edition was sold with an extra pink heart-shaped 10" vinyl, inside a PVC sleeve, featuring the singles "High School Sweethearts" and "Strawberry Shortcake". On October 6th, 2015, Melanie shared her experience with writing a hook for a hip-hop song initially two days ago, (October 4 th, 2015). Includes a 16-page vinyl sized booklet, with photos from the film -directed by Melanie Martinez (2)-, lyrics an credits for each song.In the booklet that came out with physical copies of K-12, " High School Sweethearts" was misspelled as "High School Sweathearts" and " Recess" was misspelled as "Reccess". It was later revealed on January 8 th, 2020, via Melanie's Instagram story that the deluxe version would be released in the format of an extended play titled After School. There are currently 16 songs that were intended for K-12, but only some of them made the final cut, (3 tracks are unreleased, and 13 tracks are released).

In an interview with V Magazine, Melanie confirmed that a deluxe version will likely be available in 2020. Melanie initially changed the tracklist to contain 6 songs, and ultimately decided to stick with 7 songs in July 2020, with original singles “Fire Drill” and “Copy Cat” removed from the tracklist. She originally planned to release the project in the spring of 2020, but the project ended up being released on September 25, 2020. The longest song on K-12 is " High School Sweethearts", at 5 minutes and 11 seconds, while the shortest song is " Class Fight", lasting for 2 minutes and 41 seconds. There are 13 tracks on the CD, and a separated 7 additional tracks, also known as After School, for the deluxe version.New characters would be introduced and the album would be based off of Cry Baby's experiences there. According to Melanie, "You're not learning about her, you're learning about the place that she's in and her perspective". Hype sticker, attached to the front shrink wrap, says: "MELANIE MARTINEZ - K-12 - FEATURING "STRAWBERRY SHORTCAKE" AND "LUNCHBOX FRIENDS" - SPECIAL POP-UP INSIDE - PINK VINYL - 075678657481". Beginning in September 2019, Melanie promoted the album by having the pink school bus from the film drive around the world, stopping at various locations to sell exclusive merchandise.