Learn Hardcore Indonesian: Kami melakukan penelitian kecil di kelas.

kami = we (excluding the person you’re talking to)
→ the listener is not part of the group.
kita = we (including the person you’re talking to)
→ the listener is part of the group.

In Kami melakukan penelitian kecil di kelas, the speaker is saying that they and their group did the research, but the listener was not part of it.

If the listener had joined the research, you would say:

Kita melakukan penelitian kecil di kelas.
= We (you and I / all of us here) did a small research project in class.

Does this sentence mean “we did”, “we are doing”, or “we do” a small research project?

Indonesian verbs generally do not show tense (past, present, future) the way English verbs do. The verb melakukan stays the same, and tense is understood from context or from time words.

So Kami melakukan penelitian kecil di kelas can mean:

We did a small research project in class. (past)
We are doing a small research project in class. (present, ongoing)
We do a small research project in class. (habitual, e.g., every semester)

To make the time explicit, you add time expressions:

Kemarin kami melakukan penelitian kecil di kelas.
= Yesterday we did a small research project in class.
Sekarang kami melakukan penelitian kecil di kelas.
= Right now we are doing a small research project in class.
Besok kami akan melakukan penelitian kecil di kelas.
= Tomorrow we will do a small research project in class.

What exactly does melakukan mean, and what is its base form?

Melakukan roughly means to do / to carry out / to perform (an action). It is a transitive verb, so it normally needs an object:

melakukan penelitian = to do/carry out research
melakukan tugas = to do a task
melakukan percobaan = to perform an experiment

Morphologically:

Root: laku (related to doing, acting, behaving)
lakukan: root + -kan, meaning “to do (something)”
melakukan: meN-
- lakukan → a verb meaning “to do / to carry out (something)”

For learning purposes, you can remember simply:
melakukan + noun ≈ to do / carry out + noun.

Could I say Kami meneliti di kelas instead? What is the difference between melakukan penelitian and meneliti?

Yes, you can say Kami meneliti di kelas, and it is grammatically correct.

melakukan penelitian = literally to do/carry out research
meneliti = to research / to investigate / to examine carefully

In practice:

Kami melakukan penelitian kecil di kelas.
Sounds like: We conducted a small research project in class.
Slightly more noun-based: “do a piece of research.”
Kami meneliti di kelas.
Sounds like: We did research in class / We researched (something) in class.
More verb-based: “research (actively).”

The first version (melakukan penelitian kecil) makes it clearer that you are talking about a specific “small study” or “small project” rather than just the activity of researching in general.

Why is it penelitian kecil (noun then adjective) and not kecil penelitian, as in English “small research”?

In Indonesian, the normal word order is:

noun + adjective

So:

penelitian kecil = small research (literally: research small)
kelas besar = big class
buku baru = new book
mobil merah = red car

Putting the adjective before the noun (like kecil penelitian) is not standard Indonesian and sounds wrong. So you must say:

penelitian kecil, not kecil penelitian.

Does kecil here mean physically small, short, simple, or something else?

In penelitian kecil, kecil is usually understood more metaphorically as:

small-scale
simple
not very extensive or not very serious/major

So penelitian kecil suggests something like:

a small project
a simple classroom study
a mini research activity

It does not usually mean the research is physically small; it refers to the scale/importance/complexity of the research.

Why do we use di before kelas? How is di different from ke and pada?

Di, ke, and pada are different prepositions.

di = at / in / on (location, where something happens)
- di kelas = in class / in the classroom
- di rumah = at home
- di meja = on the table
ke = to (direction, movement towards)
- ke kelas = to the class / to the classroom
- pergi ke rumah = go to the house
pada = at / on / in (more abstract or formal, often for time, topic, or recipient)
- pada hari Senin = on Monday
- pada siswa-siswa = to the students (formal)

In Kami melakukan penelitian kecil di kelas:

di is correct because it marks location: the research is done in the class.

What is the difference between di kelas and di dalam kelas?

Both are correct but slightly different in nuance:

di kelas
- Common, neutral
- Can mean in class (as an activity/lesson) or in the classroom (as a place), depending on context.
di dalam kelas
- Literally: inside the class / inside the classroom
- Emphasizes the inside-ness of the physical room, often contrasting with outside.

Examples:

Kami melakukan penelitian kecil di kelas.
= We did a small research project in class. (normal, simple)
Di luar hujan, jadi kami tetap di dalam kelas.
= It was raining outside, so we stayed inside the classroom.

In your sentence, di kelas is the most natural everyday choice.

Does kelas mean “classroom” (the room) or “class” (the group or course) here?

Kelas can mean both, depending on context:

The physical room → classroom
- Di kelas sangat panas. = It’s very hot in the classroom.
The teaching group / level / course → class
- Saya ada kelas bahasa Indonesia jam 9.
  = I have an Indonesian class at 9.
- Dia di kelas 8. = She is in 8th grade.

In Kami melakukan penelitian kecil di kelas, it is naturally understood as in class / in the classroom context—the research was done as a classroom activity. The exact nuance (room vs course) is not very important here.

Should there be a word like sebuah before penelitian kecil? Is Kami melakukan sebuah penelitian kecil di kelas more natural?

Both sentences are grammatically correct:

Kami melakukan penelitian kecil di kelas.
Kami melakukan sebuah penelitian kecil di kelas.

Notes:

sebuah is an indefinite classifier/determiner (roughly “a / one (piece of)” for countable things).
Adding sebuah can emphasize that it is one specific research project.

Differences in feel:

Kami melakukan penelitian kecil di kelas.
Natural and common; the number (one vs several) is left a bit vague, but usually understood as one unless context says otherwise.
Kami melakukan sebuah penelitian kecil di kelas.
Slightly more explicit: a small research project. Can sound a bit more formal or deliberate.

In everyday speech, leaving out sebuah is very common and perfectly natural.

How do we know if penelitian is singular or plural here? Could it mean “small research projects”?

Indonesian nouns usually do not change form for singular vs plural. Context tells you which is meant.

penelitian kecil can mean:
- a small research (project/study)
- small research (in general)

If you clearly want the plural, you add a word that shows plurality:

beberapa penelitian kecil = several small research projects
banyak penelitian kecil = many small research projects

So:

Kami melakukan penelitian kecil di kelas.
Normally understood as one small research project in that class.
Kami melakukan beberapa penelitian kecil di kelas.
Clearly means several small research projects in class.

Can I move di kelas to the beginning, like Di kelas, kami melakukan penelitian kecil? Is that still correct?

Yes, that is correct and natural.

Both of these are grammatical:

Kami melakukan penelitian kecil di kelas.
Di kelas, kami melakukan penelitian kecil.

Indonesian word order is flexible. Putting di kelas at the beginning:

Di kelas, kami melakukan penelitian kecil.

adds a little emphasis on the location (“In class, we did a small research project”). It might be chosen if you are contrasting it with another location, or continuing a narrative focused on the classroom.

Both versions are good; the original is the most neutral.