Depois da aula, a escola toda ficou vazia.

Because da is the contraction of de + a.

• depois de = after
• a aula = the class / the lesson

So:

• depois de a aula → contracted in normal Portuguese to depois da aula

This kind of contraction is extremely common in Portuguese:

• de + o = do
• de + a = da
• de + os = dos
• de + as = das

So Depois da aula literally comes from After the class.

In Brazilian Portuguese, aula usually means class, lesson, or sometimes lecture, depending on context.

In this sentence, Depois da aula most naturally means:

• After class
• After the lesson
• After the class ended

If the context is a school building, English often says after class, even though Portuguese uses the article: depois da aula.

Because Depois da aula is an introductory time expression.

It sets the scene first:

• Depois da aula, ... = After class, ...

The comma is very natural here, just like in English with introductory phrases:

• After class, the whole school became empty.

In informal writing, some people may leave it out, but with this sentence the comma is standard and clear.

Both are possible, but they can feel slightly different.

• a escola toda = the whole school / the entire school
• toda a escola can also mean the whole school, but depending on context it may sound a bit more emphatic or slightly more formal/literary.

In everyday Brazilian Portuguese, noun + todo/toda is very common when you mean the entire thing:

• o dia todo = the whole day
• a noite toda = the whole night
• a escola toda = the whole school

So this word order is very natural.

Toda agrees with escola, which is:

• feminine
• singular

So we get:

• a escola toda

Compare:

• o prédio todo = the whole building
• as salas todas = all the classrooms / the classrooms all together
• os alunos todos = all the students

The form changes to match the noun:

• todo = masculine singular
• toda = feminine singular
• todos = masculine plural
• todas = feminine plural

Because vazia is an adjective describing a escola, and adjectives usually agree in gender and number with the noun they describe.

• a escola = feminine singular
• so the adjective must also be feminine singular: vazia

Examples:

• o quarto ficou vazio = the room became empty
• a sala ficou vazia = the room/classroom became empty
• as ruas ficaram vazias = the streets became empty

So vazia matches escola.

Ficou is from ficar, and here it means became.

So:

• a escola toda ficou vazia = the whole school became empty

This suggests a change of state: before, it was not empty; after class, it became empty.

Compare:

• ficou vazia = became empty
• estava vazia = was empty
  This describes a state, without focusing on the change.
• foi vazia would not sound natural here.

So ficou is the right choice because the sentence is about what happened after class ended: the school changed from occupied to empty.

Yes, very common.

It often means to become + adjective:

• ficar triste = to become sad
• ficar feliz = to become happy
• ficar cansado = to become tired
• ficar vazio = to become empty

In this sentence:

• ficou vazia = became empty

This is one of the most useful patterns in Portuguese.

Yes. A escola inteira ficou vazia is completely natural and means almost the same thing.

Compare:

• a escola toda = the whole school
• a escola inteira = the entire school / the whole school

In many contexts, they are interchangeable.

A tiny nuance:

• toda is extremely common and conversational
• inteira can sometimes feel a bit more emphatic, as in the entire school

But both are correct.

It depends on context.

By itself, aula can mean:

• one lesson/class period
• class in a more general sense
• sometimes the school session that just ended

In this sentence, because it says the whole school became empty, the most likely interpretation is:

• after classes were over
• after the school day ended
• after that class period that caused everyone to leave

So the exact scope comes from context, not from the word aula alone.

Yes, that is a good literal translation.

But in more natural English, you would often say:

• After class, the whole school was empty.
• After class, the whole school became empty.
• Once class was over, the whole school emptied out.

The Portuguese sentence clearly uses a change idea with ficou, so became empty or emptied out captures that especially well.

It breaks down like this:

• Depois da aula = time expression, After class
• a escola toda = subject, the whole school
• ficou = verb, became
• vazia = adjective, empty

So the pattern is:

time expression + subject + verb + adjective

Or more literally:

After class, the whole school became empty.

It sounds completely natural.

In speech, native speakers may pronounce it smoothly like this:

• Depois da aula, a escola toda ficou vazia.

A few natural spoken features:

• depois da often flows together very smoothly
• escola toda also links naturally in speech
• the stress is especially noticeable in au of aula, co of escola, to of toda, and zi of vazia

Overall, this is a very normal, everyday Brazilian Portuguese sentence.