Learn Hardcore German: Die Lehrerin hört die Mitschüler und Mitschülerinnen lachen, obwohl sie leise sprechen. - The teacher hears the male and female classmates laughing, although they are speaking quietly.

Feminine singular (it agrees with Lehrerin), and
Nominative (because die Lehrerin is the subject of the sentence: she is doing the hearing).

So die in die Lehrerin tells you both the gender of the noun (feminine) and its grammatical role (subject in nominative singular).

Why is it die Mitschüler und Mitschülerinnen? Why do we list both forms?

German has gendered nouns for people:

der Mitschüler = (male) classmate
die Mitschülerin = (female) classmate

In the plural:

die Mitschüler = male classmates or mixed-gender group (traditionally generic)
die Mitschülerinnen = female classmates

When you say die Mitschüler und Mitschülerinnen, you are explicitly naming both male and female classmates. This is often done for gender-inclusive language, to make clear that all genders are meant, not just “default male”.

Today you also see shorter “inclusive” spellings like:

die Mitschüler*innen
die Mitschüler:innen

but your sentence just spells both out fully: Mitschüler und Mitschülerinnen.

Why is the article also die in die Mitschüler und Mitschülerinnen? Is that nominative or accusative?

Here die Mitschüler und Mitschülerinnen is the object of the verb hört (hears), so it is in the accusative plural.

In German, the plural article die looks the same for nominative and accusative:

Nominative plural: die Kinder spielen – “the children are playing”
Accusative plural: die Lehrerin hört die Kinder – “the teacher hears the children”

So you know it’s accusative not from the form of die, but from the role in the sentence:

Subject (who hears?) → die Lehrerin (nominative)
Object (whom does she hear?) → die Mitschüler und Mitschülerinnen (accusative)

Why is it hört die Mitschüler und Mitschülerinnen lachen and not something like hört, dass die Mitschüler lachen?

German allows two ways to express this idea:

Perception verb + object + infinitive
- Die Lehrerin hört die Mitschüler lachen.
  Literally: “The teacher hears the classmates laugh.”
  This is a very natural, compact way; English usually uses “-ing”: “hears the classmates laughing.”
Perception verb + (wie / dass) + full clause
- Die Lehrerin hört, wie die Mitschüler lachen.
- Die Lehrerin hört, dass die Mitschüler lachen.

Differences:

hört … lachen focuses on the immediate perception of the action, like English “hears them laughing.”
hört, dass … is more like “she learns / becomes aware that…”. It can be more factual and less “sensory”.

In everyday speech, hören + object + infinitive is very common with things you literally perceive with your senses.

Why is lachen in the infinitive here and not conjugated (e.g. lachen vs lachen sie)?

With verbs of perception (like sehen, hören, fühlen) German often uses a bare infinitive together with an object:

Ich höre die Kinder lachen. – I hear the children laughing.
Sie sieht den Hund rennen. – She sees the dog run(ning).

Structure in your sentence:

Finite verb (conjugated): hört (3rd person singular)
Object: die Mitschüler und Mitschülerinnen
Infinitive describing what they are doing: lachen

You do not conjugate lachen because the conjugated verb in the clause is already hört; lachen is part of the infinitive construction after the perception verb.

Why is there no zu before lachen? I learned that German infinitives often use zu.

You’re right that many infinitive constructions use zu, but there is a group of special verbs that usually take a bare infinitive (without zu). Important ones include:

sehen (to see)
hören (to hear)
fühlen (to feel)
lassen (to let)
helfen (in older/less standard usage also without zu, but today often with zu)

So you say:

Die Lehrerin hört die Mitschüler lachen. ✅
Ich sehe ihn kommen. ✅

But with many other verbs, you would need zu:

Sie versucht, leise zu sprechen. – “She tries to speak quietly.”
Er beginnt zu lachen. – “He starts to laugh.”

So zu lachen would be wrong in this particular structure with hören + object + infinitive.

Why is there a comma before obwohl and why does sprechen go to the end?

Obwohl is a subordinating conjunction (like weil, dass, wenn). These conjunctions:

Introduce a subordinate clause, and
Send the conjugated verb to the end of that clause.

That’s why you have:

…, obwohl sie leise sprechen.

Word order in the obwohl-clause:

Conjunction: obwohl
Subject: sie
Adverb: leise
Verb (conjugated, final): sprechen

The comma is required to separate the main clause (Die Lehrerin hört … lachen) from the subordinate obwohl-clause.

In obwohl sie leise sprechen, who does sie refer to? The teacher or the classmates?

Formally, sie (lowercase) can mean:

she (3rd person singular feminine), or
they (3rd person plural).

In your sentence, context decides:

The teacher hears the classmates laughing,
although they speak quietly.

So sie refers back to die Mitschüler und Mitschülerinnen and means “they”.

If it meant “she” = the teacher, the sentence would be strange:
“The teacher hears the classmates laughing, although she is speaking quietly.” – that doesn’t really make sense logically. So native speakers automatically interpret sie here as they.

Could I change the word order and say obwohl sie sprechen leise?

No, not in a subordinate clause.

In a subordinate clause introduced by obwohl, the conjugated verb must go to the very end:

✅ obwohl sie leise sprechen
❌ obwohl sie sprechen leise

In a main clause, you can say:

Sie sprechen leise. – They speak quietly.

But once you introduce obwohl, it turns into a subordinate clause, and sprechen must be final. Other elements like leise stay before the verb in the “middle field”.

What is the difference between leise sprechen and ruhig sprechen or langsam sprechen?

All three are adverb + sprechen, but they describe different qualities:

leise sprechen – to speak quietly, with a low volume.
ruhig sprechen – to speak calmly, not nervously or excitedly.
langsam sprechen – to speak slowly, at a low speed.

In your sentence, leise sprechen emphasizes the low volume – they’re speaking quietly, but the teacher still manages to hear them laugh.

Why are Lehrerin, Mitschüler, Mitschülerinnen capitalized?

In German, all nouns are capitalized, regardless of where they appear in the sentence.

die Lehrerin – noun → capitalized
die Mitschüler – noun → capitalized
die Mitschülerinnen – noun → capitalized

Adjectives, verbs, adverbs, etc. are not capitalized in normal usage:

hört, lachen, leise, sprechen – all lowercase.

Why is the German in the present tense here, although in English I’d probably say “is hearing / are speaking / are laughing”?

German usually uses the simple present to cover both:

English simple present (she hears) and
English present progressive (she is hearing).

So:

Die Lehrerin hört … can mean:
- “The teacher hears …” or
- “The teacher is hearing …”

Similarly:

sie sprechen leise = “they speak quietly” / “they are speaking quietly”
sie lachen = “they laugh” / “they are laughing”

Context usually makes it clear that this is a current, ongoing situation, even though German doesn’t change the verb form.