Mein stiller Mitschüler verlässt den Seminarraum, ohne eine Wortmeldung zu machen.

Because Mitschüler is masculine singular nominative, and it comes after mein, which is an ein-word.

In this pattern, the adjective takes the ending that shows the case/gender clearly:

• mein stiller Mitschüler = nominative masculine singular
• meinen stillen Mitschüler = accusative masculine singular

So -er on stiller is the correct ending here.

Because mein Mitschüler is the subject of the sentence, so it is in the nominative case.

For a masculine noun in the nominative, the possessive determiner is:

• mein Bruder
• mein Lehrer
• mein Mitschüler

Meiner can stand on its own as a pronoun, as in Meiner ist schon da = Mine is already here, but that is not what is happening here.

Because den Seminarraum is the direct object of verlässt.

The verb verlassen takes the accusative case, so:

• der Seminarraum = nominative
• den Seminarraum = accusative

In this sentence, the classmate is leaving the seminar room, so the room is the object being acted on grammatically.

The infinitive is verlassen, but in the 3rd person singular present tense it changes stem vowel:

• ich verlasse
• du verlässt
• er/sie/es verlässt

So verlässt is correct because the subject is mein stiller Mitschüler, which is he.

This kind of vowel change is common in some German strong verbs.

No. Verlassen is inseparable.

That means the prefix ver- stays attached:

• Er verlässt den Raum.

Not:

• Er lässt den Raum ver. ✘

Many verbs with ver- are inseparable.

This is an infinitive clause with ohne ... zu.

It means without doing something.

Structure:

• ohne + object/complement + zu + infinitive

So:

• ohne eine Wortmeldung zu machen = without making a contribution / without saying anything in discussion

Other examples:

• ohne zu sprechen = without speaking
• ohne etwas zu sagen = without saying anything
• ohne den Lehrer zu fragen = without asking the teacher

Because in an ohne ... zu clause, the subject is usually understood to be the same as the subject of the main clause.

So here:

• Mein stiller Mitschüler verlässt den Seminarraum
• ohne eine Wortmeldung zu machen

The understood subject of zu machen is still mein stiller Mitschüler.

In English we do the same thing:

• He leaves the room without saying anything.

We do not repeat he in the second part either.

Because after ohne in this kind of construction, German uses an infinitive with zu, not a finite verb.

So you get:

• ohne ... zu machen
• ohne ... zu sprechen
• ohne ... zu gehen

A conjugated form like macht would need its own full clause and subject, which is not the structure used here.

Wortmeldung is a common academic or classroom word for a contribution, comment, or request to speak.

In many contexts, it refers to speaking up in class or in a discussion.

So eine Wortmeldung machen means something like:

• make a comment
• contribute to the discussion
• speak up

It is more formal and context-specific than just etwas sagen.

German often uses noun + machen expressions where English might prefer a simple verb.

For example:

• eine Frage stellen = ask a question
• einen Vorschlag machen = make a suggestion
• eine Wortmeldung machen = make a contribution / speak up

So this is a natural collocation in German.

That said, a simpler version is also possible:

• ..., ohne etwas zu sagen.
• ..., ohne zu sprechen.

Those sound a bit more general, while eine Wortmeldung machen specifically suggests not participating in the discussion.

Because ohne eine Wortmeldung zu machen is an infinitive clause, and in this sentence it is separated by a comma.

In modern German, infinitive clauses with um, ohne, or anstatt are normally set off with a comma.

So:

• ..., ohne eine Wortmeldung zu machen.

That comma is standard and expected here.

No. German still usually means quiet, silent, or reserved, not English still meaning motionless.

So mein stiller Mitschüler means:

• my quiet classmate
• my reserved classmate

If you wanted motionless/stationary, German would usually use words like stillstehend or other context-specific expressions instead.

Yes, absolutely.

• Mein stiller Mitschüler verlässt den Seminarraum, ohne etwas zu sagen.

That is very natural and probably more common in everyday German.

The difference is nuance:

• ohne etwas zu sagen = without saying anything at all
• ohne eine Wortmeldung zu machen = without making a contribution / without speaking up in the discussion

The original sentence sounds a bit more formal and classroom-oriented.

The main clause follows normal German word order:

• Mein stiller Mitschüler = subject
• verlässt = verb
• den Seminarraum = object

Then comes the infinitive clause:

• ohne eine Wortmeldung zu machen

So the pattern is:

• Subject + finite verb + object + infinitive clause

Inside the infinitive clause, the verb goes to the end:

• ohne eine Wortmeldung zu machen

That final verb position is very typical in German subordinate structures.