Learn Hardcore Croatian: Stajali smo pred školom i čekali pravi trenutak da joj zahvalimo na pomoći. - We stood in front of the school and waited for the right moment to thank her for the help.

In Croatian past tense, the auxiliary biti (to be) in forms like sam, si, je, smo, ste, su is a clitic. Clitics normally go in second position in the clause, not necessarily right before the main verb.

Stajali smo pred školom… – correct, neutral.
Mi smo stajali pred školom… – also correct; mi is the first element, smo is second, then the main verb.
Smo stajali pred školom… – ungrammatical in standard Croatian, because nothing comes before smo to host it in second position.

So the pattern is:

(Optional element like mi) + auxiliary clitic (smo) + main verb (past participle).

In this sentence, Stajali is the first element, so smo naturally comes second: Stajali smo…

What is the difference between stajali smo and stali smo?

The verbs stajati and stati are different:

stajati – to (be) stand(ing), to be in a standing position; imperfective, focuses on ongoing state or duration.
- stajali smo pred školom = We were standing / We stood (for some time) in front of the school.
stati – to stop, to come to a stop, to start standing; perfective, focuses on the moment of change.

Compare:

Stali smo pred školom.
= We stopped in front of the school. (We came to a stop there.)
Stajali smo pred školom.
= We were there in a standing/lingering position for some time.

In your sentence the idea is of waiting around, not just the instant of arrival and stopping, so stajali smo is the natural choice.

Why does čekali not have smo after it? Why not čekali smo?

Croatian often does not repeat the auxiliary in coordinated predicates. The one smo can “serve” both past participles:

Stajali smo pred školom i čekali pravi trenutak…

Literally: “We were standing in front of the school and (we) were waiting for the right moment…”, but the second smo is dropped because it is understood.

All of these are grammatical, with slightly different emphasis:

Stajali smo pred školom i čekali pravi trenutak… – most natural.
Stajali smo pred školom i čekali smo pravi trenutak… – also possible, but you usually repeat smo only if you want to emphasize or contrast the two actions.

So the missing smo after čekali is normal and very common.

Why is it pred školom and not pred školu?

The preposition pred can govern instrumental or accusative, and the choice depends on meaning:

Instrumental = location / being somewhere:
- stajati pred školom – stand in front of the school.
Accusative = movement / direction (towards a position):
- izaći pred školu – go out (to a place) in front of the school.

In your sentence, they are already in front of the school; it’s a static location, so pred + instrumental is used:

pred školom (instrumental, singular: školom).

If it described going to that place, you would see the accusative:

Došli smo pred školu. – We came (to a spot) in front of the school.

What’s the difference between pred školom and ispred škole?

Both are possible and mean basically “in front of the school”, but with different prepositions and cases:

pred školom
- pred
  - instrumental (školom)
- a bit more neutral/formal; common in standard language.
ispred škole
- ispred
  - genitive (škole)
- very common in everyday speech, slightly more colloquial in feel.

In this sentence, you could say:

Stajali smo pred školom…
Stajali smo ispred škole…

Both are fine; the difference is subtle and stylistic rather than about meaning.

Why is školom in that form? What case is it?

Školom is the instrumental singular of škola.

Declension (singular) of škola:

Nominative: škola (school – subject form)
Genitive: škole
Dative: školi
Accusative: školu
Vocative: školo
Locative: školi
Instrumental: školom

Because pred in a static, locational meaning takes instrumental, you get:

pred školom – in front of the school.

Why is it pravi trenutak and not something like točan trenutak?

In English you say “the right moment”; Croatian uses the same idea:

pravi trenutak = the right / suitable / appropriate moment.

You could say:

odgovarajući trenutak – an appropriate moment (more formal),
točan trenutak – the exact moment (more about precision).

But the common idiomatic expression for “waiting for the right time to do something” is:

čekati pravi trenutak (da…) – to wait for the right moment (to…).

So pravi here means “suitable / perfect for our plan”, not “true vs false”.

Why is it da joj zahvalimo and not an infinitive like zahvaliti joj?

Croatian often uses da + present tense where English uses an infinitive (to thank her).

da joj zahvalimo – literally “that we thank her”, functionally “(in order) to thank her / so that we can thank her”.

You could also say:

…i čekali pravi trenutak zahvaliti joj na pomoći.

This is grammatically possible, but in many regions and in more neutral style, da + present is more natural for expressing purpose in this kind of sentence.

Rough guideline:

After modal or phase verbs (htjeti, morati, moći, početi, prestati…), infinitive is very common:
Želimo joj zahvaliti. – We want to thank her.
For standalone “in order to” clauses of purpose, da + present is very common:
Čekali smo pravi trenutak da joj zahvalimo.

What does joj mean here, and why not njoj?

Joj is the unstressed (clitic) dative form of ona (she). It means “to her”:

zahvaliti nekome – to thank someone (to someone)
→ zahvaliti joj – to thank her.

Croatian has stressed and unstressed forms of these pronouns:

Dative singular feminine:
- njoj – stressed (used for emphasis or when pronounced alone)
- joj – unstressed clitic (normally used inside sentences)

In your sentence, the neutral, unstressed clitic is expected and it must appear in the clitic “cluster” position after da:

da joj zahvalimo – neutral, normal.
da se njoj zahvalimo – adds emphasis to njoj: to her (and not someone else).

So joj is correct and preferred here; njoj would be used only if you want to particularly stress “to her”.

Should there be a se in zahvalimo? Is da joj zahvalimo correct without se?

The verb is usually given as zahvaliti (se) nekome na nečemu.

With se: zahvaliti se nekome na pomoći – to express thanks to someone for the help (slightly more explicit/polite).
Without se: zahvaliti nekome na pomoći – also used and accepted, especially in everyday speech.

Both are common; many speakers don’t feel a big difference. If anything:

zahvaliti se sounds a bit more formal/polite.
zahvaliti sounds a bit more neutral/shorter.

So:

da joj zahvalimo na pomoći – correct.
da joj se zahvalimo na pomoći – also correct, maybe a bit more ceremonious or careful.

Why is it zahvalimo (present tense) when the rest of the sentence is in the past?

In Croatian, da-clauses often use the present tense even when referring to a future action relative to the past.

Main clause (past):
Stajali smo pred školom i čekali pravi trenutak…
– We were standing and waiting.
da-clause (present form, future meaning):
da joj zahvalimo na pomoći
– (so that) we could / would thank her for the help.

The present in a da-clause functions somewhat like an English subjunctive or “would”/“could”:

Čekali smo da joj zahvalimo.
= We waited so that we could thank her.

So the tense difference is natural and expected: past in the main clause, present (with future reference) in the da-purpose clause.

Why is it na pomoći and not za pomoć?

The standard pattern with zahvaliti and hvala is:

zahvaliti se nekome na nečemu
hvala ti na pomoći

So:

na
- locative (here: pomoći) is the regular construction:
  zahvaliti joj na pomoći – to thank her for the help.

Za pomoć is sometimes heard, influenced by English for or other Slavic patterns, but in Croatian the idiomatic and prescriptive choice with zahvaliti is na:

Hvala na pomoći. – Thanks for the help.
Zahvaljujem vam na pomoći. – I thank you for the help.

That’s why the sentence has na pomoći, not za pomoć.

Why does pomoć appear as pomoći here? Is this a verb or a noun?

Here pomoći is a noun form, not the verb.

There are two different words:

pomoć – noun, “help”
pomoći – verb, “to help” (perfective infinitive)

In your sentence:

na pomoći = na
- locative of the noun pomoć.

Declension (singular) of the noun pomoć:

Nominative: pomoć
Genitive: pomoći
Dative: pomoći
Accusative: pomoć
Vocative: pomoći
Locative: pomoći
Instrumental: pomoći

So pomoći here is locative after the preposition na (for which the pattern is na + locative when it introduces the thing you are thanking for). The meaning is clearly “help”, not “to help”.

Why are the past forms stajali and čekali ending in -i? What if the speakers are all women?

In Croatian, the past participle agrees with the subject in gender and number.

Base forms here:

stajao (m sg), stajala (f sg), stajalo (n sg)
čekao (m sg), čekala (f sg), čekalo (n sg)

Plural:

Masculine (or mixed group): stajali, čekali
Feminine group only: stajale, čekale

In your sentence:

Stajali smo… i čekali…
This implies that the group is either all male or mixed gender.

If the speakers are all female, you would say:

Stajale smo pred školom i čekale pravi trenutak da joj zahvalimo na pomoći.

The pronoun smo (we) doesn’t change; the agreement happens in the participle endings -i (masc/mixed) vs -e (fem).