Study Group

Director

• 
  Lee Jang Hoon

Screenwriter

• 
  Oh Bo Hyun

Main Role

• 
  Hwang Min Hyun

  Yun Ga Min

  Main Role
• 
  Han Ji Eun

  Lee Han Gyeong

  Main Role
• 
  Cha Woo Min

  Pi Han Ul

  Main Role
• 
  Lee Jong Hyun

  Kim Se Hyeon

  Main Role
• 
  Shin Su Hyun

  Lee Ji U

  Main Role
• 
  Yoon Sang Jung

  Choi Hui Won

  Main Role
• 
  Gong Do Yu

  Lee Jun

  Main Role

Support Role

• 
  Ju Yeon U

  Kim Sun Cheol

  Support Role
• 
  Baek Seo Hoo

  Ma Min Hwan [Yeonbaek Gang]

  Support Role
• 
  Hong Min Gi

  Park Geon Yeop [1st year student]

  Support Role
• 
  Park Yoon Ho

  Lee Hyeon U [Ji U's twin / 1st year student]

  Support Role
• 
  Kim Young Ah

  Jeon Mi Hyeon [Ga Min's mother / Director of Korean Taekwondo Association]

  Support Role
• 
  Jung Jae Sung

  [Vice-principal]

  Support Role
• 
  Shim Yoon Bo

  Na Tae Man [Detective]

  Support Role
• 
  Kim Hwi Gyu

  No. 173

  Support Role
• 
  Ri Min

  [Dean of students]

  Support Role
• 
  Jin Woo Jin

  Kim Gyu Jin [Disciplinary Committee member]

  Support Role
• 
  Seo Min Je

  Kang Tae O

  Support Role

Guest Role

• 
  Lee Jung Hyuk

  Pi Yeon Baek (Ep. 1)

  Guest Role
• 
  Kang Du Hyun

  [Student] (Ep. 1)

  Guest Role
• 
  Yang Joon Seok

  [Student] (Ep. 1)

  Guest Role
• 
  Song Won Su

  [Security guard] (Ep. 2 )

  Guest Role
• 
  Kim Min Ah

  Hwang Mi Hui (Ep. 3)

  Guest Role
• 
  Lee Nam Gyeong

  Lee Ji U [Child] (Ep. 3)

  Guest Role
• 
  Jo Yi Hyun

  Lee Hyeon U [Child] (Ep. 3)

  Guest Role
• 
  Kim Dong Gyun

  Hwang Do Gyun (Ep. 4)

  Guest Role
• 
  Song Seung Hwan

  Lee Jun [Teen] (Ep. 4)

  Guest Role
• 
  Kang Ji Yong

  Lee Jun [Child] (Ep. 4)

  Guest Role
• 
  Cho Yi An

  Anti [Young teen] (Ep. 4)

  Guest Role
• 
  Kim Min

  O Jang Ho [Yeonbaek Gang] (Ep. 4)

  Guest Role
• 
  Dok Ko Kwang

  [Pedestrian thug] (Ep. 4)

  Guest Role
• 
  Lee Chang In

  Nam Sang U (Ep. 4-5)

  Guest Role
• 
  Ma Hyun Ji

  Hong Jae Hui (Ep. 4-5)

  Guest Role
• 
  Shin Seo Woo

  Kim Se Hyeon [Child] (Ep. 4-5)

  Guest Role
• 
  Lim Ji Sub

  Anti (Ep. 4, 10)

  Guest Role
• 
  Seo In Geol

  Jang Bi Hwan (Ep. 4, 7)

  Guest Role
• 
  Kim Jung Young

  O Jeong Hwa [Former teacher] (Ep. 4, 9-10)

  Guest Role
• 
  Mo Geon Hu

  Kook Gwan U [Black warehouse 1st grade] (Ep. 4, 7)

  Guest Role
• 
  Lee Ung Jae

  Yoo Jun Min (Ep. 5)

  Guest Role
• 
  Lee Keun Wook

  Kang Dong Su (Ep. 5)

  Guest Role
• 
  Lee Dong Gi

  Eom Seok Dae (Ep. 5)

  Guest Role
• 
  Choi Ye Chan

  Kim Ho Min [Child] (Ep. 5)

  Guest Role
• 
  Kyung Ki Hyun

  [Delinquent] (Ep. 5)

  Guest Role
• 
  Lee Jae Yong

  [Delinquent] (Ep. 5)

  Guest Role
• 
  Jo Seung Yun

  [Dean of academic affairs] (Ep. 5, 9-10)

  Guest Role
• 
  Yang Hee Woo

  [Driver] (Ep. 6)

  Guest Role
• 
  Kim Min Chae

  [Real estate agent] (Ep. 6)

  Guest Role
• 
  Ko Gyeong Man

  [Hospital employee] (Ep. 7)

  Guest Role
• 
  Kang Yoon

  Chae Seon Ho (Ep. 7-8)

  Guest Role
• 
  Park Jae Hwi

  Kim Jae Seung (Ep. 7-8)

  Guest Role
• 
  Kim Nak Gyun

  Chu Seong Ung (Ep. 7-8)

  Guest Role
• 
  Kim Sung Ho

  [Guard] (Ep. 7-8)

  Guest Role
• 
  Jeon Moo Song

  [Sun Cheol’s grandfather] (Ep. 7-8)

  Guest Role
• 
  Oh Han Kyul

  Park Geon Yeop [Child] (Ep. 9)

  Guest Role
• 
  Seo Soo Min

  [Student] (Ep. 9)

  Guest Role
• 
  Ma Jung Pil

  [Hui Won’s dad] (Ep. 9)

  Guest Role
• 
  Kim Mi Ra

  [Hui Won’s mother] (Ep. 9)

  Guest Role
• 
  Park Jin

  Bang Sang In (Ep. 9-10)

  Guest Role
• 
  Lim Su Hwan

  [Secretary] (Ep. 9-10)

  Guest Role
• 
  Kang Ji Hoon

  [Anchorman] (Ep. 9-10)

  Guest Role
• 
  Park Jun Hyuk

  Anti [Teen] (Ep. 10)

  Guest Role
• 
  Jang Joo Young

  Kim Ho Min

  Guest Role
• 
  Lee Jong Wook

  Park Jung Nam

  Guest Role
• 
  Park Jung Hoon

  Heo Jeong Min

  Guest Role
• 
  Choi Seung Hoon

  Yun Ga Min [Teen]

  Guest Role
• 
  Jang Sun Yool

  Yun Ga Min [Child]

  Guest Role
• 
  Han Jung Hoon

  Park Min Cheol [3rd student]

  Guest Role
• 
  Park Jun Woo

  [Bully]

  Guest Role
• 
  Shin Min Soo

  [Custodian]

  Guest Role
• 
  Jang Eui Don

  [Superintendent]

  Guest Role
• 
  Kim Young Woong

  [Se Hyeon's father]

  Guest Role
• 
  Lee Young Joon

  [Yusung tech student]

  Guest Role
• 
  Seo Dong Kyu

  [Yusung tech student]

  Guest Role

Cameo

• 
  Lee Jong Hyuk

  Pi Yeon Baek [Han Ul's father]

  Cameo
• 
  Yoo In Soo

  Chu Jae Hwang [Student] (Ep. 9-10)

  Cameo

Unknown

• 
  Lee Ryu Min Unknown