Poco a poco, me fui tranquilizando al escuchar la voz de mi profesora.

Poco a poco means little by little, gradually, or step by step.

The repetition is part of the fixed expression. You do not usually translate it word for word as little to little. It simply means that something happened progressively, not all at once.

In this sentence, it tells you that the speaker gradually became calmer.

Both are possible, but they express slightly different ideas.

• Me fui tranquilizando suggests a gradual process:
  I was gradually calming down / I slowly became calmer
• Me tranquilicé sounds more like a completed change:
  I calmed down

The structure ir + gerundio often shows something that develops over time.

So:

• Me fui tranquilizando = the calming down happened bit by bit
• Me tranquilicé = I calmed down, without emphasizing the process as much

This matches very well with poco a poco.

The me is there because tranquilizarse can be used as a pronominal/reflexive-style verb meaning to calm down.

Here, me refers to the speaker:

• me fui tranquilizando = I gradually calmed down

It does not always need to mean a literal reflexive action like I calm myself in a deliberate sense. In Spanish, many verbs use these pronouns to express a change of state in the subject.

Compare:

• tranquilizar algo = to calm something
• tranquilizar a alguien = to calm someone
• tranquilizarse = to calm down

Fui is the preterite of ir:

• yo fui = I went

But in me fui tranquilizando, it is not really about physically going somewhere. It is part of the verbal structure ir + gerundio, which shows gradual development over time.

So here:

• fui tranquilizando does not mean I went calming
• it means something more like I became calmer little by little

This is a very common pattern in Spanish:

• Fue mejorando = He/She gradually improved
• Fui entendiendo = I gradually came to understand
• Se fue haciendo tarde = It gradually got late

Tranquilizando is the gerund of tranquilizar.

In Spanish, the gerund is often used after verbs like ir, seguir, andar, or estar to describe an ongoing or developing action.

Here, ir + gerundio gives the idea of progressive change:

• me fui tranquilizando = I gradually calmed down

So the gerund is important because it helps show that the calming happened over a period of time, not instantly.

Al + infinitive is a very common Spanish structure meaning:

• when ...
• upon ...
• on ...-ing

So:

• al escuchar la voz de mi profesora = when I heard my teacher’s voice / upon hearing my teacher’s voice

It often expresses that one action happens at the moment another happens.

More examples:

• Al llegar, me llamó. = When he arrived, he called me.
• Al verlo, sonreí. = When I saw him, I smiled.

Both escuchar and oír relate to hearing, but they are not exactly the same.

• oír = to hear
  more about perceiving sound
• escuchar = to listen (to)
  more about paying attention to a sound

In real usage, though, escuchar can sometimes sound natural even where English would simply say hear, especially when the sound has an emotional effect or is meaningful.

In this sentence, al escuchar la voz de mi profesora suggests that hearing the teacher’s voice had a calming effect, and it can feel slightly more intentional or more focused than oír.

That said, al oír la voz de mi profesora would also be possible.

In Spanish, possession is often expressed with de:

• la voz de mi profesora = my teacher’s voice / the voice of my teacher

You do not add an extra possessive like mía here, because mi profesora already shows whose teacher she is.

So:

• la voz de mi profesora = correct
• la voz de mi profesora mía = incorrect

Spanish often prefers this structure:

• el coche de mi padre = my father’s car
• la casa de mi amiga = my friend’s house

Both can refer to a female teacher, but they are used a bit differently.

In Spain:

• profesor / profesora is the general word for teacher, especially in secondary school, university, and often in many other educational settings
• maestro / maestra is more associated with primary school teachers, though usage can vary

So mi profesora sounds very natural here, especially if the speaker is talking about a school or academic teacher in a general sense.

Yes, Spanish word order is flexible.

The original sentence:

• Poco a poco, me fui tranquilizando al escuchar la voz de mi profesora.

is natural because it starts with the idea of gradual change, which is an important part of the meaning.

You could also say:

• Me fui tranquilizando poco a poco al escuchar la voz de mi profesora.
• Al escuchar la voz de mi profesora, me fui tranquilizando poco a poco.

These versions are also correct, but they place the focus slightly differently.

The original version sounds smooth and natural because poco a poco sets the scene right away.

It uses the preterite in the verb fui plus a gerund:

• me fui tranquilizando

This normally presents the gradual calming as something that happened in a completed past situation.

If you used the imperfect, for example:

• me iba tranquilizando

that would sound more like I was gradually calming down, perhaps as background description, or as something ongoing in a larger past scene.

So the difference is roughly:

• me fui tranquilizando = a completed gradual process in the past
• me iba tranquilizando = an ongoing gradual process in the past, often descriptive

Not very well. A very literal version such as:

• Little by little, I went calming myself upon hearing the voice of my teacher

is understandable, but it sounds unnatural in English.

More natural English translations would be:

• Little by little, I calmed down when I heard my teacher’s voice.
• I gradually calmed down on hearing my teacher’s voice.
• Hearing my teacher’s voice gradually calmed me down.

This is a good example of how Spanish and English often express the same idea with different grammar.