Learn Hardcore Indonesian: Setelah sidang sekolah tentang aturan baru, hakim siswa dan pelatih debat membuat sinopsis hasil diskusi. - After the school hearing about the new rules, the student judge and the debate coach make a synopsis of the discussion results.

So sidang sekolah tentang aturan baru is a formal school meeting/hearing held to discuss new rules.
Using sidang for a formal school meeting is natural and not strange in Indonesian.

Does tentang aturan baru describe the school or the hearing? Why is it placed there?

Tentang aturan baru attaches to sidang, not to sekolah.

Structure: sidang [sekolah] [tentang aturan baru]
Meaning: a school hearing about the new rules, not a school about new rules.

If you want to make the attachment extra clear, you could also say:

sidang sekolah mengenai aturan baru
sidang sekolah tentang peraturan baru

But the original word order is already normal and unambiguous to native speakers: tentang aturan baru is understood to modify sidang.

What does hakim siswa mean exactly? Why is it hakim siswa, not siswa hakim?

Hakim siswa means student judge, i.e. a judge who is a student (for example, in a mock trial, a student court, or a debate competition).

In Indonesian, the typical pattern is:

Head noun
- modifier noun

So:

hakim siswa = judge (who is a) student
guru bahasa = language teacher
pelatih debat = debate coach

If you say siswa hakim, it sounds more like a student of judges or a student who studies judges, which is not what you want.
So hakim siswa is the natural order when the main identity is judge and siswa just specifies what kind of judge.

Is pelatih debat different from guru debat? Why use pelatih here?

Yes, there is a nuance:

pelatih = coach, trainer
- Focus on training skills, drills, practice, strategy.
guru = teacher
- Focus on formal teaching in a classroom/subject.

For a debate team, pelatih debat is very natural, because this person coaches the students for competitions, like a sports coach.
Guru debat could be understood, but it sounds more like a school subject teacher whose subject is debate. The sentence suggests a team or activity context, so pelatih debat is the better choice.

Are hakim siswa and pelatih debat singular or plural here? There is no seorang or plural marker.

Indonesian does not always mark singular or plural explicitly; context decides.

In this sentence, hakim siswa dan pelatih debat is most naturally understood as:

one student judge and one debate coach.

If you wanted to make singular explicit, you could say:

seorang hakim siswa dan seorang pelatih debat

For plural, you could say:

para hakim siswa dan para pelatih debat
or use hakim-hakim siswa dan pelatih-pelatih debat

But without any marker, Indonesian leaves it open; in many narratives, the default reading is singular unless context suggests a group.

What does membuat sinopsis mean here? Is sinopsis just summary? Could we use ringkasan instead?

Membuat sinopsis literally means to make a synopsis. In everyday use:

sinopsis = a concise outline or brief summary, often of a story, film, or complex content.
ringkasan = a more general word for summary.

In this context, membuat sinopsis hasil diskusi means they created a brief summary/outline of what came out of the discussion.

You could say:

membuat ringkasan hasil diskusi
This is also natural and maybe a bit more neutral.

Sinopsis may sound slightly more formal or technical, but it is not wrong here.

Why is it sinopsis hasil diskusi, and not sinopsis dari hasil diskusi? Is there a difference?

Both are possible, but there is a nuance:

sinopsis hasil diskusi
- Literally: synopsis [of the discussion’s result]
- Compact noun phrase: sinopsis
  - hasil diskusi (synopsis of the discussion’s outcome).
sinopsis dari hasil diskusi
- Literally: synopsis from the result of the discussion
- Slightly longer, more explicit, but a bit less compact in style.

Indonesian commonly links nouns directly like sinopsis hasil diskusi without dari, especially in written or formal style.
So the original version sounds natural and slightly more concise.

How does setelah work here? Why is there a comma after the first clause?

Setelah is a subordinating conjunction meaning after (in time).

Structure of the sentence:

Setelah sidang sekolah tentang aturan baru,
→ time clause: After the school hearing about the new rules,
hakim siswa dan pelatih debat membuat sinopsis hasil diskusi.
→ main clause: the student judge and the debate coach made a synopsis...

When a setelah-clause comes first, it is common to put a comma before the main clause:

Setelah ... , [main clause].

You could also reverse the order without a comma:

Hakim siswa dan pelatih debat membuat sinopsis hasil diskusi setelah sidang sekolah tentang aturan baru.

Both word orders are correct; the original simply foregrounds the time frame.

There is no past tense marker like sudah. How do we know this happened in the past?

Indonesian normally does not require explicit tense markers. Time is often shown by:

context
time expressions (like kemarin, besok, tahun lalu)
conjunctions like setelah (after), sebelum (before), ketika (when)

Here, setelah already implies a sequence:

First: the hearing happens.
Then: they make the synopsis.

So it is naturally understood as a past sequence in most contexts.
You could add sudah or telah for extra clarity/formality:

... hakim siswa dan pelatih debat telah membuat sinopsis hasil diskusi. But it is not necessary.

Could we use sesudah instead of setelah? Is there any difference?

Yes, you can substitute sesudah for setelah without changing the meaning:

Sesudah sidang sekolah tentang aturan baru, hakim siswa dan pelatih debat membuat sinopsis hasil diskusi.

Differences:

setelah is slightly more common in everyday usage.
sesudah is perfectly correct, maybe a bit more formal or old-fashioned in some regions, but still widely used.

In most modern contexts, they are interchangeable.

What is the meaning of aturan in aturan baru, and how is it formed?

Aturan means rule(s) or regulation(s).

Morphology:

Root verb: atur = to arrange, to organize, to regulate.
Nominal suffix: -an
atur
- -an → aturan = the thing that arranges / the regulation.

So aturan baru = new rules / a new regulation.
You might also see peraturan, which is a related, often slightly more formal form:

peraturan sekolah = school regulations
aturan sekolah = school rules

In many everyday cases, aturan and peraturan are interchangeable.

What does hasil diskusi mean exactly? Is hasil “result” in a general sense?

Yes, hasil is a general word for result, outcome, product, yield.

hasil ujian = exam result
hasil panen = harvest yield
hasil rapat = the outcome of a meeting

So hasil diskusi is the outcome/result of the discussion:
the conclusions, decisions, or points agreed on during the discussion.

Can this sentence be turned into the passive voice in a natural way?

Yes, a common passive version would be:

Setelah sidang sekolah tentang aturan baru, sinopsis hasil diskusi dibuat oleh hakim siswa dan pelatih debat.

Here:

sinopsis hasil diskusi becomes the subject.
dibuat is the passive form of membuat.
oleh hakim siswa dan pelatih debat marks the agents (who did it).

Both the active original and this passive version are natural; the choice depends on whether you want to focus on who did it (active) or on what was done (passive).