The Cast of ‘Teach You A Lesson’ on Show’s Success and Impact

If you’ve been following our watchlist recommendations, you’ll know we’ve made no secret of our love for Teach You A Lesson. It’s a show that entertains, certainly, but more importantly, it sparks conversations with its unflinching willingness to confront issues that are often difficult to discuss. 

Through its gripping narrative, the series shines a light on the devastating realities of school violence, the failings of institutions meant to protect victims, and the immense pressures placed on students within an unforgiving education system. 

The K-drama remains in the Top 10 Most-Watched TV Shows in Malaysia more than a month since its premiere. With audiences across the globe continuing to embrace both its compelling story and its timely social commentary, Teach You A Lesson has become much more than just another hit drama (pun fully intended). 

Ahead, we speak to the cast consisting of Kim Moo-yul, Lee Sung-min, Jin Ki-joo, and Pyo Ji-hoon, as well as director Jong Hong-chan to talk about Teach You A Lesson’s remarkable success, the conversations it has inspired, and what it means to be part of a series with an enduring message. 

Kim Moo-yul as Na Hwa-jin 

What was the first thing that drew you to your character when you read the script? 

What stood out to me was the reason Na Hwa-jin helped establish the ERPB and the way he continues to live his life afterwards. I was drawn to his desire to become a better adult, his willingness to keep striving, and the strong sense of responsibility he carries as he dedicates himself to protecting the educational environment. 

Na Hwa-jin has some intense fight choreography and action scenes in the show. How did you prepare for the physicality of your role? 

I trained consistently throughout filming to build the physicality I felt Na Hwa-jin needed. I also spent a lot of time rehearsing with my fellow actors so we could create action scenes that felt both natural and satisfying. At the same time, it was important to show that Hwa-jin was carrying on the educational values his late fiancée, Ga-yoon, believed in. That’s why I approached each action scene differently depending on who he was facing. 

When dealing with students, I deliberately kept the physical contact to a minimum—even something as light as a playful flick on the forehead—whereas with adult perpetrators, I worked with my scene partners to deliver action that felt much more powerful and decisive. 

Did you take inspiration from the original webtoon, or did you also have a hand in moulding a different type of Na Hwa-jin for this live adaptation? 

I wanted to build my own version of Na Hwa-jin for this live-action adaptation of Teach You A Lesson. I spent a lot of time thinking about how to make him feel as authentic and believable as possible, and I had many conversations with the director throughout the process. Together, we carefully shaped every aspect of the character—from his personality and the way he delivered his lines to his reactions in each moment. 

Was there a moment where you felt you finally “became” Na Hwa-jin, rather than just playing him? 

I think it was in Episode 10, when Hwa-jin says to Gyu-cheol, “Let’s try again.” That line felt comforting not only for Gyu-cheol, but also for Hwa-jin himself—and for me as well. It was a scene where a lot of emotions came together, and I think that was the moment I felt closest to truly becoming the character. 

What has been the best part of playing Na Hwa-jin? 

What I loved most was how many different sides Na Hwa-jin has. He adjusts the way he uses force depending on who he’s dealing with, but outside of those intense moments, he also has a playful sense of humour and enjoys making the people around him laugh. Those contrasting qualities made him feel like a genuinely human and relatable character to me. 

What has been the funniest or most unexpected reaction from international fans that made you smile? 

The one that has stayed with me the most was a message from a teacher in Malaysia. They told me the series really resonated with them and that it brought them both comfort and encouragement. Knowing that the story connected with someone across borders and cultures, and that they genuinely embraced the series, was incredibly comforting to me as well. 

Did playing your character spark any changes or make you think differently about justice, authority, education, relationships, family, or friendships?

In many ways, yes. Above all, it made me think much more deeply about education. The issues surrounding education are incredibly complex—even experts find them difficult to navigate. Playing Na Hwa-jin allowed me to look at many of today’s social issues from different perspectives, and that was a meaningful experience for me.

If there is a season 2, what would you like to see explored with your character?

If there were a second season, I’d love to explore how Na Hwa-jin continues to grow and how he moves forward in his work with the Bureau for the Protection of Educational Rights. This season was largely about him confronting his past and ultimately choosing to forgive Gyu-cheol. In a new season, I’d like to see Hwa-jin take the next step—having made peace with his past and continuing to evolve as a person.

Lee Sung-min as Choi Gang-seok

What was the first thing that drew you to your character when you read the script? 

More than the character himself, I was drawn to the strength of the story. It was also my second project with director Hong Jong-chan, so I already had a great deal of trust in him. That trust gave me even more excitement and curiosity about taking on the role. 

Did playing your character spark any changes or make you think differently about justice, authority, education, relationships, family, or friendships? 

It definitely made me much more interested in education. I was already aware that there were many challenges within the education system, but this project allowed me to examine those issues more deeply and reflect on them from a broader perspective. 

What is one scene that best represents who your character really is? 

For me, the line in Episode 4—“The ERPB stands neither with teachers nor with students. We stand with the victims.”—best captures Choi Gang-seok’s core values and the essence of who he is. 

While you play a commanding Minister of Education, he’s also a grieving father. How important was it to also show this side of your character to audiences? 

I wanted to remain as faithful to the script as possible. More than anything, I felt it was important for viewers to see Choi Gang-seok first and foremost in his public role. Rather than openly expressing his personal grief, I tried to portray him as someone who carries that pain quietly within himself while continuing to fulfil his responsibilities. 

At the end of the story, do you think Gang-seok sees himself as someone who succeeded, someone who failed, or something in between? 

I think he would say he’s still a work in progress. The ERPB can’t solve every problem in society, and injustice will always exist. We’ll have to keep working to address those challenges. What’s most important is not giving up, but continuing to move forward and do what we can to make things better. 

Fans love the dynamic between you and Kim Moo-yul that ranges from emotional to comedic. Were there any surprising moments or improv between you two that made it into the final take? 

This was already my third project with Kim Moo-yul, so we had developed such a strong rapport that we could almost communicate with just a look. Rather than one particular behind-the-scenes story, what I found most interesting was that in Juvenile Justice we played two judges, while in Teach You A Lesson we reunited as the Minister of Education and an inspector from the ERPB. 

He’s an actor who reinvents himself with every project, and I found myself constantly admiring his transformation throughout filming.

Jin Ki-joo as Im Han-rim

What was the first thing that drew you to your character when you read the script? 

I was drawn to how straightforward she is. Han-rim knows exactly what she likes and dislikes, has a clear sense of right and wrong, and never wavers in her convictions. I found that simplicity and certainty incredibly appealing. 

What do you think is Ha-rim’s greatest strength, even if she doesn’t always recognise it herself? 

Her purity. Han-rim is someone with an incredibly pure heart. It’s that purity that fuels her passion, allows her to admire and respect someone wholeheartedly, and gives her the strength to stay true to her convictions. That’s what I love most about her. 

Fans also love your screams and outbursts throughout the show. Was it difficult to perfect that screeching volume every time? 

There were days when several of those scenes were scheduled back-to-back, but thankfully I managed just fine. I think seeing the director and crew enjoy those moments gave me even more energy, so I was able to fully commit to each scene. 

Did playing your character spark any changes or make you think differently about justice, authority, education, relationships, family, or friendships? 

It didn’t really change the way I think. More than anything, it simply left me hoping that each of us would fulfil our responsibilities. I think the world would be a much better place if we all did that. 

Audiences adore the love line between you and Pyo Ji-hoon’s character. How did both of you build chemistry off-set? 

Pyo Ji-hoon has a way of making everyone around him feel comfortable. He’s kind, warm, and full of positive energy, so we naturally became close while working together. 

Your character is said to be a combination of two characters from the original webtoon. Since there was no true 1:1 from the source material, how did you shape the character for this adaptation? 

I stayed as faithful to the script as possible. Ultimately, the answers to who Han-rim is were already there in the screenplay. My job was to trust what I found in the script and focus on bringing those qualities to life in the most authentic way I could. 

The ERPB almost runs like a family unit. How did all of you develop chemistry and trust to portray these dynamics on screen? 

There was a lot of improvisation on set. We constantly built on one another’s ideas, and I think that’s what made the ERPB feel so warm and human. Kim Moo-yul, in particular, came up with so many ad-libs, and they always gave me even more to work with as an actor. 

For example, before one action scene, I improvised having Han-rim tie her hair back. Kim Moo-yul immediately responded with, “You’re tying your hair up… We’re not here to kill someone, are we?” That one line made my little improvisation so much funnier and richer. There were so many moments like that throughout filming. 

Pyo Ji-hoon as Bong Geun-dae

What was the first thing that drew you to your character when you read the script? 

I was immediately drawn to the chance to play someone as intelligent as Geun-dae. Beyond that, he has many personality traits that are very different from my own, which made the role even more appealing. I saw it as an opportunity to challenge myself as an actor and explore a side of myself I hadn’t shown before. 

How are you different from and similar to the characters you play? 

First of all, Geun-dae is much smarter than I am. (laughs) I’m not particularly academic or naturally intelligent, so I think that’s the biggest difference between us.

Did playing your character spark any changes or make you think differently about justice, authority, education, relationships, family, or friendships? 

Rather than changing my perspective, the role made me realise that I should be the first to reach out to people around me who might need help—whether they’re younger colleagues, family members, or friends I can support. It reminded me that sometimes the most important thing is simply to be there for someone when they need you. 

Bong Geun-dae brings a different energy to the ERPB team with his gentle and scaredy-cat nature. But what do you think is Geun-dae’s biggest strength? 

I think Geun-dae’s greatest strength is his willingness to take action despite his fears. Even if he’s thinking to himself, “Can I really do this?” it’s never easy to turn those doubts into action. But no matter what mission he’s given, Geun-dae never backs down from the challenge. 

What’s even more impressive is that when the moment comes, he often performs far better than anyone expects. That tells me he has incredible hidden potential. So I believe his greatest strengths are his willingness to take action and the untapped potential he carries within him. 

Bong Geun-dae is not a character that exists in the original webtoon. How did you shape and build this entirely new character for the show? 

The first step was having countless conversations with the director to better understand who Bong Geun-dae was and how we wanted to shape him. At his core, he’s someone who always gives his all, but the character really came to life through his interactions with everyone on set. 

Whether he was trying to impress Gang-seok or building relationships with Hwa-jin, Han-rim, and the rest of the team, Geun-dae gradually became a much richer and more layered character. I also felt that one of his defining traits was his genuine reactions whenever he encountered someone intimidating. 

I worked very hard to make those moments feel as authentic as possible, and I’m grateful that viewers seemed to enjoy that side of him. 

Was there a moment where you felt you truly understood Geun-dae as a person? 

There was a scene where Hyeong-ju, who had once been bullied, was sitting down with those same classmates at a snack bar, talking together peacefully. It was the moment when Geun-dae could see, with his own eyes, that they had genuinely changed through the ERPB’s efforts. Watching that transformation unfold made me feel proud and deeply moved. That was the moment I felt I truly understood Geun-dae’s heart. 

Director Hong Jong-chan

Teach You A Lesson became the No. 1 non-English show on Netflix in over 90 countries. Why do you think it has resonated so much with people all over the world?

There’s a saying: “It takes a village to raise a child.” Raising and educating children is a challenge shared by families everywhere. At the same time, issues like school violence, bullying, and the shortcomings of public education are certainly not unique to Korea. 

I think the series resonated because it combined those universal realities surrounding education with the catharsis that genre storytelling can provide. Many viewers may have been feeling powerless in the face of these long-standing problems that seem impossible to solve in real life, and Teach You a Lesson offered them a sense of catharsis through fiction. 

More than anything, it was incredibly meaningful to see audiences beyond Korea connect with the heart of the story and understand what we were trying to say.

These themes are not unique in K-dramas. With Teach You A Lesson, what did you particularly pay close attention to showcase these themes in a different light?

What sets Teach You a Lesson apart is that, while it deals with the very real issue of education, it introduces the fictional ERPB as a fantasy element. I wanted to portray the harsh realities of collapsing respect for teachers and school violence with honesty and emotional weight, but whenever the ERPB stepped in, I wanted those moments to feel exhilarating—almost like watching a classic action adventure. 

The idea that this organisation directly intervenes on behalf of victims to resolve situations that no one else can in real life is the driving force of the story. 

It was also important to me that this wasn’t simply the story of a lone hero. The series is powered by its ensemble. Behind Na Hwa-jin’s commanding presence, Choi Gangseok bears the weight of protecting the team, Im Han-rim fights alongside him on the front lines, and Bong Geun-dae brings warmth and humanity to the group. 

Each character stands with victims in their own way, and I believe that dynamic is what makes the series’ blend of social realism and genre storytelling feel convincing. 

You’ve also directed Juvenile Justice, which similarly deals with adolescent violence and crime. What is it about this topic that continues to intrigue you as a director? 

I believe one of the greatest challenges facing our society today is communication. It’s a theme I expect will continue to guide the projects I choose for some time. Whether it’s communication within families, across social classes, or throughout society as a whole, many of our biggest problems begin when people fail to truly connect with one another. 

While working on Juvenile Justice, I came to realise that juvenile crime is never just about young offenders themselves. It’s deeply intertwined with families, schools, and the broader social system. Teach You a Lesson grows out of that same perspective. A story about young people is ultimately a story about families, schools, and, more broadly, the society we all live in. 

Although both series could be seen as stories about “troubled students,” I believe they are fundamentally about the consequences of failed communication. The difference lies in how they approach that idea. Juvenile Justice examines the complexity of the system through a balanced lens, while Teach You a Lesson takes a more genre-driven approach, using action and catharsis to break through that same sense of frustration. 

Teach You A Lesson is based on a popular webtoon. As a director, how did you decide on the changes you would make for this live-action adaptation? 

The most important goal in adapting the original webtoon was to preserve its emotional resonance around the issue of violations of teachers’ rights, as well as its sense of catharsis, while telling a story that felt more deeply human. I wanted every character to feel more layered and relatable by giving each of them a stronger sense of humanity. 

The series writer and I also shared the belief that the story shouldn’t simply be about punishment. Instead, we wanted it to explore what true education really means. I believe that direction aligned well with the balanced perspective I hoped to bring to the series. 

What scene looked effortless on screen but was actually the hardest to film? 

Without a doubt, it was Choi Ga-yun’s story. 

Although her screen time is relatively limited, Ga-yun is the seed from which this entire story grows. Everything—the ERPB, Choi Gang-seok, and even Na Hwa-ji—exists because of what she stood for as both a teacher and an adult. They continue their work while carrying forward the values she believed in and remembering the example she set. 

The challenge was that we had to convey who Ga-yun was as a person and as a teacher within a relatively small amount of screen time. Her story is revealed mainly through flashbacks that explore her relationship with Gyu-cheol, so we had to express a great deal with very little.

As a director, I spent a lot of time figuring out how to weave her emotional arc naturally into the overall narrative while also preserving the mystery surrounding what had happened between her and Gyu-cheol. It remained one of the most difficult creative challenges for me until the very end. 

Thankfully, Ha-young, who played Choi Ga-yun, and Lee Bong-joon, who portrayed Cho Gyu-cheol, invested so much thought and care into those characters alongside me. Thanks to their dedication, we were able to bring that story to life in the way I had hoped. I’m deeply grateful to both of them. 

What conversation do you hope audiences have after watching the series? 

Rather than offering easy answers, I hope Teach You a Lesson leaves people with meaningful questions to think about. After watching all episodes, I hope viewers take a moment to ask themselves, “What can I do from where I stand?” 

I hope the series encourages people to reflect on the challenges facing realities today, what it takes to restore a sense of justice when the system has failed, and how much we are willing to risk in order to stand with those who have been wronged. Those are the kinds of questions I hope will continue to spark conversations long after the series ends. 

Fans are calling for a second season of the show. Are there any discussions about that already, and as a director, what other areas are you excited to potentially explore if so? 

I still feel there are many stories left to tell—both within schools and throughout our society. 

At the same time, whenever I think about my next project, I always begin with one question: “What is the story people need most right now?” Whatever the genre may be, I believe every story should ultimately be about people. 

Going forward, I hope to continue telling stories about those who have been marginalised, those who carry emotional scars, and the adults who choose to stand beside them. 

Teach You A Lesson is available to stream on Netflix.

For more recommendations on K-dramas to watch, head here.