Subí un poco el volumen porque desde atrás no oía bien a la profesora.

Because the sentence contrasts:

• a completed action: Subí un poco el volumen = I turned the volume up a bit
• a background/ongoing situation: no oía bien a la profesora = I couldn’t hear the teacher well

In Spanish, this is very common:

• preterite for the main event that happened
• imperfect for the situation or condition around it

So the idea is: I turned up the volume because I wasn’t hearing the teacher well.

Subir el volumen means to turn up the volume or to raise the volume.

It is a very common Spanish expression:

• subir el volumen = turn the volume up
• bajar el volumen = turn the volume down

So Subí un poco el volumen is a natural way to say I turned the volume up a little.

In Spanish, un poco often goes right after the verb when it modifies the action:

• Subí un poco el volumen = I turned the volume up a little

That is the most natural order here.

You could sometimes hear other word orders in Spanish, but Subí un poco el volumen is the standard, neutral phrasing.

Spanish often drops subject pronouns when the verb already makes the subject clear.

• Subí already tells us the subject is I
• so yo is not necessary

You could say Yo subí un poco el volumen, but that usually adds emphasis or contrast, for example:

• Yo subí el volumen, no Ana.

Without that emphasis, leaving out yo sounds more natural.

This is a very common learner question.

In many contexts:

• oír = to hear
• escuchar = to listen

Here the idea is about ability to hear, not the act of actively listening. So:

• no oía bien a la profesora = I couldn’t hear the teacher well

If you said no escuchaba bien a la profesora, it could sound more like I wasn’t listening well or I wasn’t properly listening to the teacher, depending on context.

So oía is the better choice here.

That is the personal a.

In Spanish, when the direct object is a specific person, you usually use a:

• oía a la profesora
• veo a mi amigo
• escuché al director

So a la profesora does not mean to the teacher here. It just marks the teacher as a person receiving the action of the verb.

Here desde atrás means something like:

• from the back
• from the back row / from the rear part of the room

In context, it suggests the speaker was sitting or located toward the back, and from there they couldn’t hear the teacher well.

In a classroom, this is very natural. Similar expressions could be:

• desde el fondo
• desde la parte de atrás

But desde atrás is short and natural.

Because porque is the conjunction meaning because.

• porque = because
• por qué = why

So:

• Subí un poco el volumen porque... = I turned the volume up because...

If it were a question, then you would use por qué:

• ¿Por qué subiste el volumen? = Why did you turn up the volume?

Bien means well, so no oía bien means:

• I wasn’t hearing well
• I couldn’t hear properly

It modifies the verb oía.

Spanish often uses bien in this kind of sentence rather than something more elaborate:

• No veo bien
• No entiendo bien
• No oigo bien

It sounds very natural.

Yes, you could, and it would still be understandable. But no oía bien a la profesora is more natural in this sentence.

Putting bien before a la profesora keeps the phrase flowing smoothly and makes it clear that bien modifies oía.

So:

• no oía bien a la profesora = most natural here
• no oía a la profesora bien = possible, but less smooth

They show the correct stress and help distinguish forms.

• subí has stress on the last syllable: su-BÍ
• oía has stress on the í: o-Í-a

In oía, the accent is especially important because it breaks what might otherwise be read as a single syllable combination. It helps show the pronunciation clearly.

For learners, it is useful to notice:

• subi would be misspelled
• oia would also be misspelled

The accents are required.

Yes. It only depends on whether the teacher is female or male.

• la profesora = the female teacher
• el profesor = the male teacher

So you could say:

• Subí un poco el volumen porque desde atrás no oía bien al profesor.

Notice that a + el = al:

• a la profesora
• al profesor

It works perfectly in Spain Spanish, and it is also understandable and natural in most other varieties of Spanish.

A few notes:

• oía is standard everywhere
• subir el volumen is standard everywhere
• profesora is standard everywhere

So although you asked about Spanish from Spain, this sentence is not especially regional. It is broadly standard Spanish.