Стоит учителю заговорить, как в классе становится тихо.

Here стоит is part of a fixed construction, not its usual everyday meaning.

The pattern is:

стоит + dative + infinitive, как ...

In this pattern, it means something like:

• it only takes ... for ...
• as soon as ...
• the moment ...

So:

Стоит учителю заговорить, как в классе становится тихо.

means roughly:

As soon as the teacher starts speaking, the classroom becomes quiet.

A more literal way to feel the structure is:

It only takes the teacher to start speaking, and the classroom goes quiet.

Also, this is different from sentences like Мне стоит это сделать, which can mean I should do it or It would be worth doing it. The presence of the second clause with как makes it clear that this is the as soon as / it only takes construction.

Because this construction requires the person doing the action to be in the dative.

So in:

Стоит учителю заговорить...

учителю means for the teacher.

The structure is not built like a normal clause with a nominative subject. It is more like:

• Стоит мне выйти, как начинается дождь.
  • As soon as I step out, it starts raining.
• Стоит детям увидеть снег, как они бегут на улицу.
  • As soon as the children see snow, they run outside.

So учителю is dative because the construction is basically saying:

It only takes for the teacher to start speaking...

not

The teacher starts speaking... as a normal finite verb clause.

Because after this use of стоит, Russian uses an infinitive to name the action that triggers the result.

So the structure is:

стоит + dative + infinitive

That is why you get:

• учителю заговорить
• not учитель заговорит
• not учитель говорит

The infinitive here does not show tense by itself. The overall sentence is understood as a general present-time pattern because стоит and становится are in the present tense.

Because заговорить means to begin speaking / to start speaking, while говорить means to speak / to be speaking more generally.

In this sentence, the important idea is the triggering moment: the teacher starts talking, and immediately the classroom becomes quiet.

That is why заговорить works so well here. It points to the start of the action.

Compare:

• заговорить = to start speaking
• говорить = to speak, to be speaking

Using говорить here would sound much less natural, because the sentence is about what happens at the moment the teacher begins to talk.

No. Here как does not mean how.

It is the second part of the paired construction:

стоит ..., как ...

In this pattern, как introduces the result that happens immediately afterward.

So the meaning is something like:

• as soon as ... , ...
• the moment ... , ...
• and immediately ...

Example:

• Стоит открыть окно, как становится холодно.
  • As soon as you open the window, it gets cold.

So in your sentence, как connects the first event with its immediate consequence.

Because the sentence contains two clauses:

1. Стоит учителю заговорить
2. как в классе становится тихо

Russian punctuation normally separates these clauses with a comma, and in this fixed construction the comma is expected.

So the pattern is written as:

Стоит ..., как ...

not as one unbroken clause.

Because тихо here is not an adjective describing a noun. It is a predicative adverb/state word, meaning quiet in the sense of it is quiet or it becomes quiet.

Russian often describes the state of a place this way:

• Здесь тихо. = It is quiet here.
• В комнате стало темно. = It became dark in the room.
• На улице холодно. = It is cold outside.

So:

в классе становится тихо

means:

it becomes quiet in the classroom

not

the classroom becomes a quiet one.

That is why тихо is correct, not тихий.

Grammatically, this is an impersonal sentence. Russian does not need to name a subject here.

The sentence focuses on the state in the classroom, not directly on the students. So:

в классе становится тихо

literally means:

in the classroom, it becomes quiet

Of course, in real-world meaning, the students are the ones falling silent. But Russian often expresses this by describing the environment or situation rather than naming the people.

So instead of saying:

the students become quiet

Russian very naturally says:

it becomes quiet in the classroom.

Because it describes a habitual or general situation: this is what usually happens whenever the teacher starts speaking.

So the present-tense forms:

• стоит
• становится

do not mean only one event happening right now. They describe a repeated pattern.

English does the same thing:

• As soon as the teacher starts speaking, the classroom becomes quiet.

If you wanted a one-time event in the past, Russian would usually shift to past forms, for example:

Стоило учителю заговорить, как в классе стало тихо.

That means:

As soon as the teacher started speaking, the classroom became quiet.

Yes, it is natural and common, though it is a bit more stylistically marked than the most basic possible wording. It gives a strong sense of immediacy and automatic result.

A simpler version could be:

• Когда учитель начинает говорить, в классе становится тихо.
  • When the teacher starts speaking, the classroom becomes quiet.

But the original:

Стоит учителю заговорить, как в классе становится тихо.

sounds more like:

• The moment the teacher starts speaking, the classroom goes quiet.
• As soon as the teacher starts speaking, the room falls silent.

So yes, it is very natural, and it is useful to learn this pattern because Russian uses it often:

• Стоит мне отвлечься, как я забываю, что хотел сказать.
• Стоит солнцу выйти, как становится тепло.