La alumna se siente más segura cuando habla en voz alta en clase.

Both are possible, but they are not exactly the same in feel.

• la alumna = the female pupil/student
• la estudiante = the student (can refer to a man or a woman, though the article shows gender: la estudiante, el estudiante)

In this sentence, alumna makes the student clearly female, and the adjective later also agrees with that: segura.

In Spain, alumno/alumna is very common in school contexts. Estudiante is also common, but it can sound a bit more neutral or general.

Sentirse is a reflexive verb meaning to feel in the sense of emotional or personal state.

• sentir = to feel, to sense
• sentirse = to feel oneself, to feel

So:

• La alumna se siente segura = The student feels confident/secure

The se is part of the verb sentirse. You usually need it when talking about how someone feels:

• Me siento bien = I feel well
• Te sientes cansado = You feel tired
• Se siente más segura = She feels more confident

Because sentir and sentirse are used differently.

• sentir often means to feel something external or physical, or to regret
  • Siento frío = I feel cold
  • Siento mucho tu pérdida = I’m very sorry for your loss
• sentirse is used for personal states or emotions
  • Me siento feliz = I feel happy
  • Se siente segura = She feels confident/secure

So in this sentence, the idea is her internal state, which is why sentirse is the natural choice.

Because adjectives usually agree in gender and number with the noun they describe.

Here, la alumna is feminine singular, so the adjective must also be feminine singular:

• seguro = masculine singular
• segura = feminine singular

Examples:

• El alumno se siente más seguro = The male student feels more confident
• La alumna se siente más segura = The female student feels more confident

It can depend on context, because seguro/segura can mean both safe and sure/confident/secure.

In this sentence, más segura most naturally means:

• more confident
• more self-assured

Because the context is speaking in class, it is about confidence, not physical safety.

So La alumna se siente más segura is best understood as The student feels more confident.

Más means more, and Spanish often allows the comparison to remain unstated if the context is clear.

So:

• se siente más segura = she feels more confident

This may imply:

• more confident than before
• more confident in that situation
• more confident than in other situations

Spanish does not need to spell out the comparison if it is understood from context.

If you wanted to make it explicit, you could say:

• más segura que antes = more confident than before

Because this sentence describes a general or habitual situation.

• cuando habla en clase = when she speaks in class

Spanish uses the present tense here just like English often does in general statements:

• She feels more confident when she speaks in class

It is not about one single future event. It means whenever that happens, this is how she feels.

In this sentence, habla naturally refers back to la alumna.

The subject is not repeated because Spanish often leaves out subject pronouns when they are clear from the verb form or context.

So:

• La alumna se siente más segura cuando habla...
• literally: The student feels more confident when speaks...
• naturally: The student feels more confident when she speaks...

Because habla is third person singular, it could grammatically mean he/she/it speaks, but here the obvious referent is la alumna.

Because Spanish is a pro-drop language, which means subject pronouns are often omitted when they are unnecessary.

So instead of saying:

• cuando ella habla

Spanish often just says:

• cuando habla

The pronoun ella would only be added for emphasis, contrast, or clarity.

For example:

• La alumna se siente más segura cuando habla = normal
• La alumna se siente más segura cuando ella habla, no cuando lee = more emphatic/contrastive

Yes, en voz alta is a very common fixed expression meaning out loud or aloud.

Literally:

• voz = voice
• alta = high/loud
• en voz alta = in a loud voice

But you should usually learn it as a whole phrase:

• leer en voz alta = to read aloud
• hablar en voz alta = to speak out loud

It is much more natural than trying to translate English word-for-word.

No, not in this expression.

It is en voz alta because voz is a feminine noun:

• la voz

So the adjective agrees with voz:

• alta, not alto

This agreement happens even though the full phrase functions like an adverbial expression.

Both can exist, but they are not always used the same way.

• en clase usually means in class / during class
• en la clase often refers more specifically to in the classroom or in the particular class

In your sentence, en clase sounds very natural because it refers to the classroom situation or class time in general.

Examples:

• Habla en clase = She speaks in class
• Está en la clase = She is in the classroom / in the class

So en clase is the most idiomatic choice here.

The given word order is very natural, but Spanish is somewhat flexible.

Standard version:

• La alumna se siente más segura cuando habla en voz alta en clase.

Possible variations:

• Cuando habla en voz alta en clase, la alumna se siente más segura.
• La alumna se siente más segura en clase cuando habla en voz alta.

These versions are still correct, but they shift the focus slightly.

The original order is smooth and neutral:

1. subject: La alumna
2. main verb: se siente
3. description: más segura
4. time/situation clause: cuando habla...

You would change the noun, the reflexive form if needed, and the adjective agreement.

For a male student:

• El alumno se siente más seguro cuando habla en voz alta en clase.

For several female students:

• Las alumnas se sienten más seguras cuando hablan en voz alta en clase.

For several male students or a mixed group:

• Los alumnos se sienten más seguros cuando hablan en voz alta en clase.

Notice the changes:

• alumna / alumno / alumnas / alumnos
• se siente / se sienten
• segura / seguro / seguras / seguros
• habla / hablan