Learn Hardcore German: Die Schülerin arbeitet konzentriert im Unterricht. - The pupil works with concentration in class.

Schülerin is the feminine form of Schüler (student, pupil).
- der Schüler = male student
- die Schülerin = female student
The article changes with gender:
- der for masculine singular
- die for feminine singular (and for all plural)

So die Schülerin tells you that the student is female.

What case is die Schülerin, and how do you know?

Die Schülerin is in the nominative case.

You know this because:

It is the subject of the sentence (the person doing the action).
In German, the subject is in the nominative.
The nominative feminine singular article is die.

So die Schülerin = the (female) student as the subject.

Why is the verb arbeitet and not something else?

The verb is arbeiten (to work).

It is conjugated in the present tense for 3rd person singular:

ich arbeite
du arbeitest
er/sie/es arbeitet
wir arbeiten
ihr arbeitet
sie/Sie arbeiten

The subject is die Schülerin (she), so you use arbeitet:
Die Schülerin arbeitet … = The (female) student works / is working …

Is konzentriert an adjective or an adverb here?

In this sentence, konzentriert functions as an adverb: it tells you how she is working.

arbeiten konzentriert = to work in a concentrated / focused way

In German, the same basic form is often used for adjectives and adverbs. Context tells you the function:

adjective: Sie ist konzentriert. (She is concentrated/focused.) – describes the noun/pronoun
adverb: Sie arbeitet konzentriert. (She works in a concentrated way.) – describes the verb

Could I say Die Schülerin ist konzentriert instead? What is the difference?

Yes, you can, but the meaning changes slightly:

Die Schülerin arbeitet konzentriert.
Focuses on the action: she is working in a focused, concentrated manner.
Die Schülerin ist konzentriert.
Focuses on her state: she is (right now) in a concentrated, focused state.

Both are natural, but the original sentence emphasizes how she is working, not just that she is in that mental state.

Why is it im Unterricht and not in dem Unterricht?

im is a standard contraction of:

in (preposition) + dem (dative article masculine/neuter) → im

Unterricht is masculine (der Unterricht), and in with a location takes the dative:

in dem Unterricht = in the class/lesson
→ contracted to im Unterricht

The full form in dem Unterricht is grammatically correct but sounds overly formal or emphatic in most contexts.

What case is Unterricht in, and why?

Unterricht is in the dative case.

Reason:

The preposition in can take dative (location) or accusative (movement/direction).
Here it means location (in class, during the lesson), so it uses the dative.
Masculine dative singular article is dem, which is contracted to im:
- in + dem Unterricht → im Unterricht

Could I say in den Unterricht instead of im Unterricht?

You can, but it means something different:

im Unterricht (dative)
= in class, during the lesson (location, time frame)
in den Unterricht (accusative)
= into the class / into the lesson (movement into something)

So Die Schülerin arbeitet konzentriert im Unterricht means she is focused during class, not that she is going into the class.

Where can konzentriert go in the sentence? Is the word order fixed?

The given order is very natural:

Die Schülerin arbeitet konzentriert im Unterricht.

Other possible orders:

Die Schülerin arbeitet im Unterricht konzentriert. – also correct, slightly different rhythm.
Im Unterricht arbeitet die Schülerin konzentriert. – emphasizes during the lesson.

General rule: the conjugated verb (arbeitet) must stay in second position in a main clause. Adverbials like konzentriert and im Unterricht are more flexible, but the original order is the most neutral.

Why don’t we add something like -ly to make konzentriert into an adverb?

German does not change the form of adjectives to make adverbs the way English does with -ly.

English: concentrated (adj) → concentratedly / in a concentrated way (adv)
German: konzentriert is used for both:
- Sie ist konzentriert. (adjective)
- Sie arbeitet konzentriert. (adverb)

So you simply use konzentriert without changing the ending.

Is konzentriert related to a verb? What is the base verb?

Yes. konzentriert is the past participle of the verb konzentrieren (to concentrate).

Verb: (sich) konzentrieren = to concentrate (oneself), to focus
Past participle: konzentriert

This participle is used:

adjectivally: eine konzentrierte Schülerin (a focused student)
predicatively: Die Schülerin ist konzentriert.
adverbially: Die Schülerin arbeitet konzentriert.

Why is Unterricht capitalized?

In German, all nouns are capitalized.

Schülerin is a noun → capitalized.
Unterricht is a noun → capitalized.
arbeitet, konzentriert, im are not nouns → not capitalized.

So Die Schülerin arbeitet konzentriert im Unterricht follows the standard rule for noun capitalization.

Could I say Eine Schülerin arbeitet konzentriert im Unterricht? What’s the difference?

Yes, that is also correct.

Die Schülerin arbeitet …
= the student works … (a specific student that the listener can identify)
Eine Schülerin arbeitet …
= a student works … (one student, not specified which one)

So it’s just the normal definite vs. indefinite article difference.

How would I say The students work concentrated in class in the plural?

You have a few options, depending on what you want to emphasize:

Feminine plural only:
Die Schülerinnen arbeiten konzentriert im Unterricht.
Masculine or mixed group plural:
Die Schüler arbeiten konzentriert im Unterricht.

arbeiten is the correct plural form with sie (they):
sie arbeiten konzentriert …

Does arbeitet mean “is working” or “works”? How do I know?

German Präsens (present tense) covers both English simple present and present progressive.

So Die Schülerin arbeitet konzentriert im Unterricht can mean:

The student works in a concentrated way in class. (habitual)
The student is working in a concentrated way in class (right now). (ongoing)

Context usually makes it clear which reading is intended.