In Korean high school, there are many classes named like this: 1-1, 1-2, 1-3, 2-1, 3-1 etc.

1-1 means first grade first class.. 2-1 means second grade first class .. something like that.
I don't think there is a grade system like my country in your country.
Anyway, I want to know how to call those classes. (one to one class? two to one class?)
moon72961-1 means first grade first class..
This is very unfamiliar to us. Could you explain the terms a little more? Is "first grade" the student's first year in high school? Is "first class" the earliest class in the morning? ( This is just a guess.) Or do the terms mean something completely different? Would the class name have a subject as well as the numbers? (Like "mathematics 1-2"?)
moon7296one to one class? two to one class?)
Regardless of what the numbers mean, I'm pretty sure this would not be the right way to say it. Maybe I can suggest something when I understand the system a little better.
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Thank you for answering my question and showed some things that readers may be not sure of.

The first "1" in 1-1 means the students' first year in high school. The second "1" in 1-1 means the one of the class out of many classes in the same grade; for example, there are 10 classes and each student belongs to one of the class. In Korea, usually students don't move to class to class but they stay in one classroom and different subject teachers come to their classrooms to teach them. So for example, English teachers can go to 1-1, 1-2, 1-3 and 1-4 classes, and other English teachers can go to 1-5, 1-6, 1-7, and so on.

Is it still unclear?
We would probably say "grade one, section one."
moon7296English teachers can go to 1-1, 1-2, 1-3
You would just pronounce the numbers: "class one-one, one-two, etc."
In the US, generally (since I was in school some variations to the following have been introduced into the educational system), you would have children, who are will not be 6 years old before Jan., starting school in Sept. as kindergarteners. The school yr. lasts from around Sept. to June. After kindergarten, they proceed to first grade, then to 2nd, 3rd, 4th, 5th, 6th, 7th, 8th, 9th, 10th, 11th, and 12th grade. Kindergarten to 6th grade is called elementary (or sometimes, grammar) school. 7th grade to 8th grade is called middle (or sometimes, junior high) school. 9th grade to 12th grade is called high (or sometimes, secondary) school. Thus, students in elementary school (kindergarten to 6th grade) will be about 5 to 11 yrs. old, those in jr. high school (7th to 8th grade) will be about 12 to 13 yrs. old, and those in high school (9th to 12 grade) will be about 14 to 18 yrs. old. Students in the first grade would be called first graders, those in 2nd grade, second graders, etc. In high school (9th to 12th grade), 9th graders are also called high school freshmen, 10th graders, sophomores, 11th graders, juniors, and 12th graders, seniors. After the 12th grade students can then go on to college, or to work or into the military.
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It is clear But I saw in a variety show maybe running man ..a person asked which class are you from and the other person said I'm from class 28 and the other said I'm from class 10 what does that mean?

But how are students placed in these class ranks? Do they base it by their scores? So if you're in class 1-7 does that mean you're some genius or???

As far as my school sorts us, it is just random, it is not based on scores. The first number (ie. the 1 in 1-7) represents the grade you are in, in high school of course. In Korea we have 3 grades in high school not four. so all of the first years would be distributed into the classes that start with 1. So classes like 1-1, 1-2, 1-3, etc. The second number (ie. the 7 in 1-7) is just a classroom number, it is not anything more than that. I hope this helps!

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Ok. Now I got it fully. It means like we are in college's first year and there are many students in first year so we'll divide them into sections. This is so simple . Don't make it more complex

You're in high schools first year and there are 400 student in first year of high school in korea. So we'll divide them into 10 sections of classes. And then they'll called so

1-1 1-2 1-3 etc.