What to Watch After Extracurricular

For similar themes - escorts but set in the adult world, double life

Heartless City / Cruel City is an adult gangster drama full of gory murders, stabbings, and excellent fight scenes. It has a twist, though - one (or more) characters you think are gangsters are actually undercover cops!! It has a small amount of romance but it produces one super-hot kiss/bed scene (by kdrama standards). I really loved the lead character in this, he was a great antihero - he tried not to be evil but the circumstances made it really hard to be good...  - u/setlib

For a female lead similar to Extracurricular's Bae Gyu Ri

The FL in Itaewon Class is pretty similar (intelligent, badass, somewhat shaky morals but overall good) - u/hotcheetosandmilk

Itaewon Class starts with a bullying incident in a high school that generates a lot of drama, so you’d probably enjoy the first two episodes. Afterwards there’s not really much crime, it’s more of a business/revenge story. But if you get hooked on the characters in the beginning, you’ll like it, it definitely has a more modern, big-city feel than most kdramas. - u/setlib

For a female lead similar to Extracurricular's Bae Gyu Ri

The closest thing I can think of is the FL in Hyena, but the setting of that TV show is very different. - u/ScofLast

Similarly unpredictable

The world of the married is very unpredictable. It’s based off of BBC’s Dr Foster.  You go WTF just happened? That was bad ass. Ok that’s crazy. Whoa. You root for certain characters and hate others with equal passion - u/prismacolorful_life

For similar vibes but darker

It's not the same, but has a similar feel to it. It's kind of creepy and psychological, and much darker than Extracurricular. It follows a guy who moves into an apartment full of suspicious people. The drama shows how the people who live with him and the people who work with him slowly drive him into insanity. Its 10 episodes as well, so it wont take long to watch. Not everyone's cup of tea, but just a suggestion. - u/Neonmarks

For similar vibes, but lite.

How to Buy a Friend - had a similar feel to Extracurricular, only a bit tamer. - u/elbenne

For similar vibes

SKY Castle has a little bit of the kids in high school but is mostly about the whole family but it kind of has the same vibe.  - u/Zen_Kaleidoscope

For similar vibes 

Class of Lies, SKY Castle, Save Me are some of the teen dramas that can turn creepy and weird like Extracurricular. - u/Aashiyahaee

Another dark high school story but from the teacher's perspective

Class of Lies - the story will suck you in and all the plot twists slaps you in the face  - u/pmfv

Class of Lies is the less R-rated version of Extracurricular - u/hearteuuu

Another unpredictable, dark, short high school drama

White Christmas - is a dark thriller with a lot of characters that you're not sure if they're becoming bad, or if they can be trusted, or who the antagonist even is.  

For a kdrama, it was way less predictable than most. I was on the edge of my seat.  - u/amnesiafakedating

Another dark high school drama which grabs you from the beginning

Solomon's Perjury. The story was very different and the actors were amazing as well. From the first episode it had a unique plot and it got better with each episode. Also the OST is absolutely beautiful. - u/unrequited_comment

Another dark high school drama with slower pacing

Beautiful World - It's slow paced, instead of fast, but it's set in a high school and there's plenty of mystery and suspense - u/elbenne

Double life, but different! 

The double life of a Mom trying to find out the truth behind her daughter's bullying by going undercover as a student. Dark Comedy

It’s not exactly in line with what you’re looking for, but Angry Mom is a great watch. It’s about a mom who gets concerned when her daughter starts getting bullied at school and goes undercover to the school as a student. The mom had a reputation for being a badass when she was in school and that plays out again as she pretends to be a student. There’s also a bunch of gang and corruption related stuff that happens. It’s a great show. - u/May0negg

Double life, but different

The double life of a child of a child kidnapped and raised to seek revenge . Action Rom-Com

City Hunter - Are you out on a lookout for a fun action romcom? Well this one delivers in spades: there's undercover spies, birth secrets, kingpins, slick spy missions and flawless action scenes all wrapped up in a romcom which oozes humor. Lee Min Ho charms with his hilarious one-liners and meticulous hairstyle, while the spunky female agent holds her own throughout the drama. The baddies (I just can't call them villains, not with those brains) are a bunch of jagged old men and there's also a handsome prosecutor, amusing side-characters and some stunning locations. And I know what you're thinking - "Is this one of those Lee Min Ho dramas I should just skip?" and the answer is a resounding no. The plot is actually well thought out and amazingly paced, all leading up to the final showdown that will probably make you tear up. - u/AlohaAlex

Double life, but different

The adorable double life of Black Ops agent turned baby sitter.  Spy/Action/Friendship/Comedy

Terius Behind Me: He may be the most elite of secret agents but none of his training has prepared him for babysitting two mischievous youngsters that know how to push all of his buttons. Excellent production value helps save this drama from campy-ness and turns it into a slick-looking, heartwarming story of people bonding together to become a team of avengers worth rooting for, whether they are solving international crimes or just making sure the kids have fun at the kids cafe.  - u/myweithisway

Another Korean story about a student living a double life (Drama)

The double life of high schooler turned CEO. Rom-com

Not really a student-slash-assassin but High School King of Savvy (RomCom drama) is about a high school student living a double life as his older brother who is a CEO in a company. - u/Bananauyu

Another Korean story about a student living a double life (Movie)

Commitment (2013) - the ML is a high school student during the day and an assassin at night for a portion of the movie - u/riddleso

Another Korean story about a student living a double life (Movie)

The movie Hwayi: A Monster Boy is fantastic. It’s about a gang of thieves who bungle a kidnapping plot and end up raising a young boy. Yeo Jin-goo does a fantastic job as the boy, now a quiet high school student who is secretly being groomed/trained to be a killer.  - u/setlib