koukou no toki, watasi ha hutago no imouto to tama ni kenka wo simasita.

とき is a noun meaning “time / when”.
In Japanese, when one noun modifies another noun, you usually connect them with の.

• 高校のとき = “the time of high school” → “when I was in high school”

So the pattern is:

• Noun + の + とき ＝ “when (it was) Noun”

You can’t say 高校とき; you need の to link the two nouns.

で is mainly a place-of-action marker (“at/in a place”), like:

• 高校で勉強しました。 – I studied at high school.

But とき itself is not the action; it’s a noun meaning “time”, so we don’t use で between 高校 and とき.
(You can say 高校のときに with に, but that’s a different question—see below.)

Both are very close in meaning, but there is a nuance:

• 高校のとき
  Literally “the time of high school.”
  → Feels like “back in high school / during my high-school years.”
  It can refer to that period of life in a broad way.

• 高校生のとき
  Literally “the time (when I was) a high school student.”
  → Slightly more focused on your status as a student.

In everyday conversation, people often use them almost interchangeably.
If you want to be very explicit that you were a student (and not, say, a teacher at a high school), 高校生のとき makes that extra clear.

Yes, 高校のときに、私は双子の妹とたまにけんかをしました。 is perfectly natural.

• とき is a noun meaning “time,” and に can mark a point or period in time.
• So 高校のときに emphasizes “at that time (when I was in high school)” as the time when the action happened.

Difference in feel:

• 高校のとき、… – neutral, very common.
• 高校のときに、… – slightly more explicit that the action happened at that time.

In many cases the difference is very small, and both are acceptable.

• は marks the topic: what the sentence is “about.”

• 私 is obvious from context in many conversations, so:

  • (私 は) 双子の妹とたまにけんかをしました。
    Omitting 私 is completely natural in Japanese.

Using は:

• 私 は 双子の妹とたまにけんかをしました。
  → “As for me, I sometimes fought with my twin younger sister.”
  It just sets “I” as the topic; no special contrast is required, but it allows contrast if needed (e.g., “I did, but my brother didn’t”).

Using が:

• 私が双子の妹とたまにけんかをしました。

  This would sound like you are emphasizing “it was I (not someone else)” who fought, or answering “Who was it that fought with her?”
  In the original sentence, that kind of emphasis is not needed, so は (or dropping 私) is more natural.

Here の links 双子 (“twin / twins”) to 妹 (“younger sister”), making 双子 an attribute of 妹:

• 双子の妹 = “younger sister who is a twin” → “my twin younger sister”

So the structure is:

• [Type/description] の [family term]

Other similar expressions:

• 双子の兄 – twin older brother
• 双子の姉 – twin older sister
• 双子の弟 – twin younger brother

The の is like a possessive/descriptor link; it’s not “of” in a strict ownership sense, but rather “the [妹] that is a [双子].”

In Japanese kinship terms, 妹 always means “younger sister” (younger than the speaker).
Even with twins, there is still a birth order—one was technically born first.

• If you are the older twin and your twin is a girl:
  • You call her 妹 → 双子の妹.
• If you are the younger twin and your twin is a girl:
  • You call her 姉 (older sister) → 双子の姉.

So 双子の妹 implies:

• The speaker is older than the twin sister (by birth order), even if the actual age difference is just a few minutes.

Yes, it’s the same particle と, but here it’s used in its “with” (comitative) function.

• 妹とけんかをしました。
  = “I had a fight with my younger sister.”

So X と V する can mean “do V with X”:

• 友だちと遊ぶ – play with a friend
• 先生と話す – talk with the teacher
• 双子の妹とけんかする – fight with my twin younger sister

This is different from listing nouns:

• りんごとバナナ – apples and bananas

Same particle, different usage (listing vs. partner/comrade in an action).

All three express frequency, but with different strengths:

• たまに – “once in a while,” “occasionally”
  → Low frequency. Suggests it does happen, but not very often.

• ときどき（時々） – “sometimes”
  → Neutral “sometimes,” more frequent than たまに.

• よく – “often,” “frequently”
  → High frequency.

So in this sentence:

• たまにけんかをしました。
  = “We fought once in a while / occasionally,”
  implying that fighting was not the usual state, just an occasional event.

In modern standard Japanese, the natural adverb is たまに.

Historically, たま is related to the idea of “rare” or “occasional,” and に turns it into an adverb:
たま（rare） + に → たまに (rarely / occasionally)

In everyday speech:

• たまに – correct, standard adverb: “once in a while.”
• たま by itself as an adverb sounds either:
  • dialectal, or
  • very casual/slangy in some contexts.

So for learners, just remember たまに as a fixed adverb meaning “occasionally.”

Both are correct:

• けんかをする
• けんかする

けんか is originally a noun (“a fight, quarrel”) that combines with する (“to do”) to form a verb.

• けんか + を + する – “to do a fight” → “to fight”
• Over time, this became a single verb: けんかする, and the を is often dropped.

This happens with many noun + する verbs:

• 勉強(を)する – to study
• 運動(を)する – to exercise
• 練習(を)する – to practice

Nuance:

• けんかをしました can sound a bit more formal/explicit about it being “a fight (as a noun) that we did.”
• けんかしました is very common and completely natural in conversation.

In this sentence, either form is fine.

You should not say 妹をけんかする. That is ungrammatical.

The usual pattern is:

• A と けんかする – “A and (I) fight” / “fight with A”

So in your sentence:

• 双子の妹とけんかをしました。
  = “I had a fight with my twin younger sister.”

You can omit the partner if it’s obvious:

• よくけんかしました。 – We fought a lot. (Partner understood from context.)

But if you mention the partner, use と, not を.

Yes, たまに is quite flexible in position. These are all natural:

1. 高校のとき、たまに双子の妹とけんかをしました。
2. 高校のとき、双子の妹とたまにけんかをしました。
3. たまに、高校のとき双子の妹とけんかをしました。 (a bit less common, but possible in context)

The main points:

• たまに usually comes:

  • at the start of the sentence, or
  • just before the main verb phrase (here, before けんかをしました or near it).

• Don’t split けんかを:

  • ✕ けんかたまにをしました – incorrect.

Your example:

• たまに双子の妹とけんかをしました。
  is perfectly natural and probably the most common alternative ordering.

• しました is the polite past of する.
• した is the plain past of する.

They both mean “did (fight)” in terms of time; the difference is only the politeness level:

• けんかをしました。 – polite; used in:
  • talking to teachers, strangers, in formal writing, etc.
• けんかした。 – plain; used:
  • with friends, family, diaries, casual narration, etc.

So you could say:

• 高校のとき、双子の妹とたまにけんかした。
  → Same meaning, just casual/plain style.

Choose しました or した depending on who you’re talking to and the overall style of your speech or writing.