Since you have 34 students I'm going to assume it's a public school class? One thing I've always found to work in public school, is to take away their precious 10 minute break between classes. Think back to when you were in middle school. Didn't it suck to not have that brief moment of social time between classes? I always give them three strikes, then make them stay 5 minutes later after the bell. If they continue acting up (very rarely), I'll stretch that out to 10 and force them to be late to their next class. It also helps to see if you can talk to their homeroom teachers. Get the names of the students who are causing the most problems and basically report them.

In your case, the problem is down to one or two students. They're controlling the behavior of the rest of the students, and for as long as those students think THEY'RE the ones in control, the other students will follow their lead. You have to take control away from them. Taking away their free time is a good start, but it's already late in the year and they've already developed "coping mechanisms" for dealing with it, which isn't good for you; however, this is mostly gonna be due to the leading problem students.

First, you'll need to speak with the your coT and their homeroom teacher to find out how far you're permitted to go. Some schools will allow you to boot them from class. Others... not so much. If you're permitted to boot them from class, try to escort them directly to their homeroom teacher. If their homeroom teacher is teaching a class at that time (find out first), then see if you can escort them to the teacher's office where they'll have to sit and wait for either their homeroom teacher, or the VP/P. But before all of this, you really need to discuss if you'll be permitted to do this with the KTs and the VP/P. Either way, you need to zero in on individual students rather than on the entire class. You only deal with the entire class AFTER you've directly removed or effectively castrated the main problem students. You need to show them AND the rest of the class that YOU'RE the one in control, not them. For that, you need to understand both student mindset and Korean hierarchy. Make them lose face, but do it in a way that the rest of the class will feel that the problem students are embarrassing themselves, and that the class is also being childish by following their lead. Example: When a student is purposely trying to make YOU lose face by saying disrespectful things and laughing while you're talking to him -- stop talking. Stare, and stare hard. Don't stop until he gets super uncomfortable. And believe me, if you stare long enough and hard enough, he will. The longer you have to stare at him before you can continue class, the sooner it becomes clear to both him and the rest of the class that he's being childish and only embarrassing himself. At this point, one of two things will happen: 1) He'll stop, or 2) his behavior will escalate to try to recover some face. In my own experience, they'll get visibly angry and try to shut you down, or they'll try to storm out of class. Either way, you react immediately by escorting him from the class OR preventing him from leaving the class without an escort. Either way, the confrontation doesn't end on HIS terms... it ends on yours. It's okay if he gets visibly upset. That's actually good for you. You just can't allow yourself to become visibly upset. You can be angry. But it needs to be controlled and systematic.

Second, no matter how much effort you put into your lessons, and no matter how badly the students behave, you have to learn not to take it personally, even if it feels personal. These are kids. Yes, they know what they're doing, and yes, the majority probably know what they're doing is wrong, but they lack the maturity level to really see exactly how it makes them appear to others outside of themselves and how it may/may not effect their futures. This is just a game to them. All they know right now is that they like feeling like they're the ones in control, and they'll try to maintain that using any means necessary. So, don't take it personally. Turn the game around on them. They're trying to show the teachers who's boss, and they'll believe they've won each battle if they see you getting upset and flustered. By all means, you can show them that you're angry -- but this must be a controlled burn, and one with consequences that they'll regret. This is something you're gonna have to establish over time, and, with proper execution and support from the school, you'll be surprised by how fast it works. But you need to show the class what can and will happen to them by making examples out of select students. You punish those students first, then the rest of the class. Rinse and repeat.

I've got more to say but I need to get somewhere.

But please, feel free to follow-up and to provide more info, including on what type of punishments you've already tried to institute outside of the free-time-removal, and what, if any, actions your school has actually done in dealing with these students. They're all low-level and misbehave in all of their classes, but I'm betting that a lot of them aren't as low-level as they pretend to be. A common Korean student tactic is to play dumb. They believe it gets them out of doing certain types of work, and that it gives them more ability to disrespect the teacher, ESPECIALLY the foreign teacher (because their excuse is why do they need to respect a teacher whom they can't understand?). The rest is potential. For as long as there's a toxic atmosphere, there's no conducive motivation to learn or to behave themselves.

I agree with Chinguetti's two posts, very very good.

Firstly, you'll find that a lot of us have been in the same situation and we've come out the other side better teachers, especially if the things you've tried have worked. 

When I taught in a girls' middle school a few years back there were ten classes in the second grade, 9 were great and 1 was filled with five girls who should never have been put together.  For all other teachers classes they messed around, the teachers even found a facebook group of their's where they discussed about how they would wind up the teachers.  My co-teacher had a lot of problems when he taught them alone and there were a few times during my class where he reacted to their winding up and they just thought it was funny, he crashed their tables and books and the minute he walked off they smiled to each other.  He'd then apologise to me for doing it.  Similar to your group, they do it to get a reaction.  In the second week I was there, the main bad girl burped loudly during class, so I scolded her.  Then when I was monitoring, she did again but about a metre from me.  'Get out!  Now'  That was it.  She didn't talk to me for the rest of the year.  I found just making the class more interesting than their fooking around made them lose interest in disrupting it because the other students were interested in studying.  She just spent the class putting on makeup.  As it was a girls middle, it had some very good students who I felt sorry for because it really messed up all their classes.  In a lot of ways, it is the same for other teachers too.  The homeroom teacher of that class was getting it the whole time.  One time, the main bad girl had her phone in class, so the homeroom teacher threw it and broke it.  Cue calls from parents complaining about their little darling's broken phone. 

I remember years ago I had one bad countryside middle school class, who I felt like giving up on, like you.  When I spoke to my mum on the phone, she bollocked me.  'You're the adult.  You're the teacher.  You're the only one who fix this!'  Since then I've always seen it as a challenge that I have to rise to, as she was right. 

Although Chinguetti wrote a lot of things, I think the idea of seeing how far you can go is a good idea.  If it is just one student who is influencing others, then I'd be up for waiting for them to act up, march them to the teachers' room (corridor is a little risky as they may walk off), plonk them down on the floor somewhere in full view with a piece of paper and make them do lines for the whole class.  When the bell goes, find them and see what they did.  If it happens again, then do it again.  No facial expressions, nothing.  You don't need to shout, silence is much better.
 In that time with the other studetns you can teach the rest of the class and I'd take a wild guess that you can get the majority of class on your side and that will take the power away from them.  Over time, I'd also expect that student to crack a little bit when they realise they don't have that same power.  In some ways, in this situation it comes down to wresting control back from them.  If your Korean is good then that is a big positive. 

You could also spend time with them outside of class, during breaktime.  It helped at my countryside school that the worst students loved football.  So at lunchtime, I'd play football together and as I can play well they liked that.  During corner kicks, I'd hold their shirts and smile and joke that way, they did it back to me.  It all helps, but it takes time.  It may be a bit late now as you probably only have 4-5 weeks or so of teaching before the winter holidays.  But if you stay next year, then they'll be second graders, right?

I think the main thing is not to take it personally, it is just a challenge that you can win.  Kids change.....hopefully    Don't lose your temper and don't react angrily to them.  See what you can do with regards to isolating the bad students.  When they are apart they are not as strong or as cocky as if they are together.  We've all been there, so can empathise completely with you.   

Are you the one who arranges the seating chart?  Can you relocate your students?  Remove someone from class?

This, to me, is the absolute first thing that you do with problem classes.  If you have bad students coming to class and they think they can just sit with their mates making the situation worse, designating seats will give you a psychological advantage.  I had one class where every week I changed the seats for the students and it worked out great.  Even at my academic high school now, I change the student's seats, a little to stop the chattering friends sit together but also I think it's nice for students to have different partners and to work with others.  I can also put the weaker students with the helpful students. 

Amy,

I received a warning for offending you with my post above.

I'm sorry.

To be honest, I don't know what offended you, exactly, but that was not my intent.

Again, my apologies.

I have the same problem.  My 1st graders are a nightmare.  It doesn't matter how great or fun the lessons are, they just will not meet me half way.  It was stressful for the first couple of weeks, but then I decided that I will just plow through my lessons best I can and not stress out about it.  Don't take their behaviors personally.  I think this is the key.  They are teenagers and they just don't give a rip.  They are also low level English students and are not used to the middle school curriculum being 1st graders.  Try to give them some ways to build on the English that they already know.  Don't make things too complicated and keep your energy level up during class.  What worked for my wild donkeys is just taking time inside and outside the classroom to get to know the students.  Show that you are interested in them and remember their names.  It's easier to control them if you know their names.  Always keep your cool and don't show that they are getting to you.  Teens can be brutal if you show any weakness.   You are not the only one with the coTeacher not getting involved in managing the students, which is primarily their job.  My coTeacher just stares into his phone the whole time. 

First year teaching here, but I have a similar problem. I think I lost too much respect in the first few nervous and kind of dry lessons, and I'm worried it'll be difficult to recover. The best lessons are the ones with lots of varied activities and quick pace, to keep them too busy to cause trouble, but even on good days I really don't feel in control at all with one class. Good luck, it's not just you 

Main thing is, don't worry and take it personally and the worst thing to do is give up with a class.  If you're new to teaching here, you'll find your groove as the months go by, you'll grab lessons from thin air that work well with your groups.  All of us would have found it difficult in the first year, unless you luck out with a great school or amazing co-ts from the start.  If you teach at multiple schools you'll always have your great groups, the ok ones and the odd bad one here and there.  But over time you'll get to know the students and they'll get used to you, but it takes a little time and patience. 

I remember when I did my CELTA in Budapest and I was a pile of nerves for all my classes.  I'd prepare my classes well, with good activities but as soon as I stepped in front of the super nice 'guinea pigs', my mind went blank and I was a shaking bag of nerves.  Every class that was.  I would physically shake. 

You have a really good idea to have various short activities for students as you should remember that students especially elementary and middle, don't want to spend 40 minutes doing the same worksheet or activity.  If you were in their position you'd think it was boring too.  So you have put yourself in their position.  I teach the classes in a fashion that I'd enjoy if I were them.  Then you'll enjoy teaching it more.  You have to keep their minds engaged but in a progressive manner using 'uppers and downers' too.

Suggestion: Place an empty chair on each side of your co-teacher. Make it a punishment: sit by 'Korean' teacher and do your work. And then keep your co on their toes by frequently yelling 'Ms/Mr xx, how is he/she doing with his/her work?'. If there are no empty chairs, tell them to bring their own.

Sidenote Suggestion: Use your co-teacher. Obviously collaboratively working together is ideal. However, I don't mind when my cos work at the back, but I only let them if I don't need them. I'm constantly sending out requests, "Ms X, how do you say this in Korean?"  "Ms X could you practice the dialogue with the student without a partner" *Ms X chatting with a student in the back when I'm trying to teach* "Ms X are we ready to start this activity?" BIG SMILES SINCERE GOODNESS

ALSO: Be oh so freaking careful with your promise to let them sit by friends. You are going to get displaced students and hurt feelings all over the place. Cause when Eunji picks Minji as her seatmate, what happens to Suji, who was previously sitting by Eunji? If she wanted to stay she's going to be mad and maybe tearful.