Learn Hardcore Portuguese (Portugal): No início da aula, a professora pede silêncio. - At the beginning of the class, the teacher asks for silence.

início – slightly more neutral/formal, very common in written and spoken language.
começo – very common in everyday speech; can sound a bit more informal, but is also standard.

In this sentence, both are correct in European Portuguese. No início da aula is just a bit more neutral.

What does the da in da aula mean?

Da is a contraction:

de + a = da

So:

de = of / from
a = the (feminine singular article)

da aula therefore means of the class.

The full pattern is:

no início de + a aula → no início da aula
(at the beginning of the class)

Why do we say da aula and not just de aula?

Portuguese normally uses the definite article (a, o, as, os) in places where English does not:

English: at the beginning of class
Portuguese: no início da aula (literally at the beginning of the class)

De aula (without the article) would sound incomplete or wrong here. The noun aula is specific (a particular class), so the article a is needed, and de + a contracts to da.

In a professora, is a a preposition (to) or an article (the)?

In a professora, a is the feminine singular definite article:

a professora = the teacher (female)

It is not the preposition a (to / at) here. You can see this because:

There is no verb that would require to in front of it.
professora is a noun; the most typical word before a noun in this position is an article.

Why do we say a professora and not just professora?

In Portuguese, especially in European Portuguese, people are often referred to with a definite article:

A professora entrou. = The teacher came in.
A Maria chegou. = Maria arrived.

So:

a professora = the teacher (that specific teacher known to speaker and listener)

Saying just professora pede silêncio would sound incomplete in this context. You can drop the article in some vocative uses (calling someone):

Professora! = Teacher!

But as the subject of the sentence, a professora is the normal, correct form.

Why professora and not professor?

Portuguese nouns for professions usually have masculine and feminine forms:

o professor = the (male) teacher
a professora = the (female) teacher

The ending -a in professora marks the feminine form. The sentence is talking about a female teacher, so a professora is used.

If the teacher were male, the sentence would be:

No início da aula, o professor pede silêncio.

What tense and person is pede, and which verb is it from?

Pede is:

Verb: pedir (to ask / to ask for)
Tense: present indicative
Person: 3rd person singular (ele / ela / você)

Mini-conjugation in the present:

eu peço – I ask / I ask for
tu pedes – you ask (informal singular, mainly in Portugal)
ele / ela / você pede – he / she / you (formal) ask(s)
nós pedimos – we ask
vocês / eles / elas pedem – you (plural) / they ask

Here, the subject is a professora (she), so we use pede.

Why is it pede silêncio and not pede por silêncio or pede para silêncio?

With pedir, Portuguese normally uses a direct object without a preposition:

pedir algo a alguém = to ask someone for something

So:

pede silêncio = asks for silence
(literally asks silence)

Pedir por silêncio or pedir para silêncio are not natural here.

You do use pedir para when it’s followed by a verb:

pede para falar mais baixo = asks (them) to speak more quietly
pede para entrar = asks to come in

Why is there no article before silêncio (why not pede o silêncio)?

Silêncio here is used in a general, uncountable sense:

pede silêncio = asks for (some) silence, silence in general.

With mass nouns like silêncio, Portuguese often omits the article when speaking in a general or non-specific way.

You could say pede o silêncio, but that would usually sound more specific or emphatic, like:

pede o silêncio de todos = asks for everyone’s silence
or referring to a particular silence already mentioned.

In everyday classroom context, pede silêncio is the standard and most natural form.

Why is the simple present (pede) used instead of something like está a pedir?

In Portuguese, the simple present is used both for:

Habits and routines (like English):
- No início da aula, a professora pede silêncio.
  = At the beginning of class, the teacher (always/regularly) asks for silence.
Actions happening right now, especially in narration or when describing scenes:
- A professora entra e pede silêncio.
  = The teacher comes in and asks for silence.

You can say está a pedir silêncio (EP) or está pedindo silêncio (BP) for an action in progress right now, but for a regular repeated action at the start of every class, pede (simple present) is the normal choice.

Could we change the word order to A professora pede silêncio no início da aula?

Yes, that is completely correct:

No início da aula, a professora pede silêncio.
A professora pede silêncio no início da aula.

Both mean the same thing. The difference is just emphasis:

Starting with No início da aula slightly highlights the time: at the beginning of class…
Starting with A professora slightly highlights the subject: The teacher…

Both orders are natural in European Portuguese.

Is the comma after aula necessary?

The comma is optional here.

No início da aula, a professora pede silêncio. ✔
No início da aula a professora pede silêncio. ✔

No início da aula is an introductory time phrase. Portuguese style guides usually recommend a comma after such phrases, but you will also see it written without a comma. Both are accepted in normal writing.

What exactly does aula mean here? Is it the same as lesson?

Aula in Portuguese usually means a class session:

the period of time when the teacher and students are together in the classroom.

So in this sentence, aula is:

class / lesson (the time block in the timetable)

It is not the content of the lesson in a book (that would more likely be lição, as in lição 3 = lesson 3 in a textbook). Here it’s the actual class period.