As alunas cujos cadernos ficaram na sala vão buscá-los amanhã.

Because alunas is a feminine plural noun meaning female students.

• a aluna = the female student
• as alunas = the female students

The article has to match the noun in gender and number:

• a / as for feminine
• o / os for masculine

So:

• as alunas = correct
• os alunos would mean the male students or the students in a mixed group
• as alunos is incorrect because the article and noun do not match

Cujos is a possessive relative pronoun. It means something like whose.

So:

• as alunas cujos cadernos ficaram na sala
  = the female students whose notebooks were left in the classroom

It connects alunas and cadernos and shows possession: the notebooks belong to the students.

This word is more formal and much more common in writing than in everyday speech.

Because cujo agrees with the thing possessed, not with the possessor.

Here:

• possessor = as alunas → feminine plural
• thing possessed = cadernos → masculine plural

So the correct form is:

• cujos cadernos

Forms of cujo:

• cujo = masculine singular
• cuja = feminine singular
• cujos = masculine plural
• cujas = feminine plural

Examples:

• o aluno cujo livro sumiu = the student whose book disappeared
• a aluna cuja mochila sumiu = the student whose backpack disappeared
• as alunas cujos cadernos ficaram na sala = the students whose notebooks stayed in the room

Because the subject of ficaram is cadernos, which is plural.

In the relative clause:

• cujos cadernos ficaram na sala

the verb agrees with cadernos, not with alunas.

So:

• o caderno ficou = the notebook stayed
• os cadernos ficaram = the notebooks stayed

That is why the sentence uses ficaram.

Na sala means in the room or in the classroom, depending on context.

It is a contraction:

• em + a = na

So:

• na sala = in the room / in the classroom

Other similar contractions:

• em + o = no
• em + as = nas
• em + os = nos

Examples:

• no carro = in the car
• na escola = at/in the school
• nas salas = in the rooms

In Brazilian Portuguese, ir + infinitive is very common for future meaning, especially in everyday language.

So:

• vão buscar = they are going to get / pick up
• buscarão = they will get / pick up

Both are grammatical, but vão buscar sounds more natural and common in spoken Brazilian Portuguese.

This structure works like:

• vou estudar = I’m going to study
• vamos sair = we’re going to leave
• eles vão chegar amanhã = they’re going to arrive tomorrow

Because the sentence uses an object pronoun attached to the infinitive.

The notebooks are the direct object, and cadernos is masculine plural, so the pronoun is os. When attached after the infinitive buscar, it becomes buscá-los.

Breakdown:

• buscar = to get / to fetch
• os = them, referring to cadernos
• buscar + os → buscá-los

This is called ênclise: the pronoun comes after the verb and is attached with a hyphen.

Why not buscar eles?

• Because eles is a subject pronoun, not the standard direct object pronoun in careful grammar.

Why not buscar os?

• In standard written Portuguese, object pronouns are usually attached in this structure: buscá-los.

In everyday spoken Brazilian Portuguese, people may say things like vão buscar eles, but that is less formal and not the standard structure taught in grammar.

Because when -los is attached to an infinitive ending in -r, the final -r drops, and an accent is added to preserve stress.

So:

• buscar + os
  becomes
• buscá-los

The same thing happens with other infinitives:

• ver + o → vê-lo
• fazer + a → fazê-la
• trazer + os → trazê-los

This is a standard spelling and pronunciation pattern in Portuguese.

Because -los refers to cadernos, not to alunas.

• alunas = feminine plural
• cadernos = masculine plural

The pronoun must agree with the noun it replaces. Since it replaces cadernos, the correct pronoun is os, which becomes -los after the infinitive.

So the idea is:

• As alunas ... vão buscar os cadernos amanhã.
• As alunas ... vão buscá-los amanhã.

Yes, but the meaning changes slightly.

Without commas:

• As alunas cujos cadernos ficaram na sala vão buscá-los amanhã.

This identifies which students you mean: specifically, the students whose notebooks were left in the room.

With commas:

• As alunas, cujos cadernos ficaram na sala, vão buscá-los amanhã.

This sounds like extra, non-essential information. It suggests you are already talking about the students, and then you add the detail that their notebooks were left in the room.

So:

• no commas = restrictive, identifies the students
• with commas = non-restrictive, adds extra information

Not very common in casual speech.

Native speakers understand it, and it appears often in formal writing, journalism, literature, exams, and educated speech. But in everyday spoken Brazilian Portuguese, people often avoid cujo and use other structures instead.

For example, instead of:

• as alunas cujos cadernos ficaram na sala

people might say something more like:

• as alunas que deixaram os cadernos na sala
• as alunas que tiveram os cadernos deixados na sala
• as alunas, os cadernos delas ficaram na sala
  (less formal and structurally looser)

For learners, it is important to recognize and understand cujo, even if you do not use it often in casual conversation.

Here buscar means to go get, to fetch, or to pick up.

In this sentence, the students are going to retrieve the notebooks that were left behind.

Depending on context, buscar can also mean:

• to look for
• to seek
• to fetch / pick up

Examples:

• Vou buscar meu irmão na escola. = I’m going to pick up my brother at school.
• Estou buscando minhas chaves. = I’m looking for my keys.

In this sentence, because the notebooks are in the room and the students will go get them, pick them up / fetch them is the most natural interpretation.

Yes.

Sala is a general word meaning room, but in school contexts it often means classroom.

So na sala could mean:

• in the room
• in the classroom

The correct translation depends on the context. If the sentence is about students and notebooks, classroom is often the most natural choice.

Because time expressions are flexible in Portuguese, and putting amanhã at the end is very natural.

You could also say:

• As alunas cujos cadernos ficaram na sala vão buscá-los amanhã.
• Amanhã, as alunas cujos cadernos ficaram na sala vão buscá-los.

Both are correct.

The end position is common when amanhã is just giving straightforward time information and is not being emphasized.

A helpful way to see it is:

• As alunas = subject
• cujos cadernos ficaram na sala = relative clause describing alunas
• vão buscá-los amanhã = main predicate

More literally:

1. As alunas = the female students
2. cujos cadernos ficaram na sala = whose notebooks stayed in the room
3. vão buscá-los amanhã = are going to fetch them tomorrow

So the sentence is built like this:

[Subject] + [description of the subject] + [main verb phrase]

This is a common structure in Portuguese, even though the relative clause can make the sentence feel dense to learners.

Not in standard grammar.

The point of cujo is to express possession neatly inside a relative clause. Standard Portuguese does not normally use que plus an extra possessive phrase in the same way.

So this is correct:

• as alunas cujos cadernos ficaram na sala

But something like:

• as alunas que os cadernos delas ficaram na sala

is not standard.

If you want to avoid cujo, you usually need to restructure the sentence more naturally, for example:

• As alunas que deixaram os cadernos na sala vão buscá-los amanhã.

That changes the structure a bit, but it sounds much more natural than trying to force que into the same pattern.