1. The first class was with my homeroom teacher, Mr. Jang.

Question

2.The first class was my homeroom teacher, Mr. Jang's class.

3. The first class was my homeroom teacher, Mr. Jang's one.

4. The first class was my homeroom teacher, Mr. Jang's.

5. My homeroom teacher, Mr. Jang taught in the first class.

6. My homeroom teacher, Mr. Jang taught us in the first class.
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Do they have the same meaning? Sentence 1 is the original sentence. Which one is similar to Sentence 1 in meaning?

Answer 1

In phrasing, 1, 5, and 6 are correct, but 5 and 6 are missing a comma each.

The others are incorrect or phrased awkwardly, mainly because of the use of the possessive.

Answer 2

Here are corrections for 2 - 6.

2.The first class was my homeroom class with Mr. Jang.

3. The first class was that of my homeroom teacher, Mr. Jang.

4. The first class was my homeroom teacher, Mr. Jang's. [can't be corrected because this is saying the class was the teacher!]

5. My homeroom teacher, Mr. Jang, taught in the first class.

6. My homeroom teacher, Mr. Jang, taught us in the first class.

In 5 and 6, "Mr. Jang" is being used as an appositive. Appositives need TWO commas (one before it and one after) unless the appositive is at the end of the sentence.
Check out appositives here: http://www.chompchomp.com/terms.htm

Answer 3

Thank you for yoiur help.
What about the following one?

4. The first class was my homeroom teacher, Mr. Jang's. class.