Læreren siger, at opførslen i klassen er vigtig.

Læreren means the teacher. Danish often adds the definite article to the end of the noun instead of using a separate word like English the.

• en lærer = a teacher
• læreren = the teacher

So -en here marks definiteness.

For the same reason: opførslen is the definite form, meaning the behavior.

• opførsel = behavior
• opførslen = the behavior

The noun opførsel takes the common-gender definite ending -en, so it becomes opførslen.

At means that and introduces a subordinate clause:

• Læreren siger = The teacher says
• at opførslen i klassen er vigtig = that the behavior in class is important

In English, that can often be left out: The teacher says the behavior...
In Danish, at is much more natural here and is normally included.

Because after at, Danish uses subordinate clause word order. In this sentence, the structure is:

• at
  • subject + other elements + verb + adjective

So:

• at
• opførslen i klassen = subject
• er = verb
• vigtig = adjective/predicative

This is different from main-clause word order, where Danish follows the V2 rule and the finite verb usually comes second.

Because vigtig agrees with the noun it describes.

Opførsel is a common-gender noun, so the adjective is:

• vigtig

Compare:

• en vigtig bog = an important book
• opførslen er vigtig = the behavior is important

If the noun were neuter, you would usually get vigtigt:

• et vigtigt emne = an important topic

I klassen literally means in the class or in the classroom, but in context it usually means in class or in the classroom environment.

So opførslen i klassen means the behavior shown during class or in the classroom.

Depending on context, Danish klasse can refer to:

• the physical class/classroom
• the group of students
• the lesson context

Because standard Danish spelling uses a comma before many subordinate clauses, including clauses introduced by at.

So:

• Læreren siger, at ...

This is normal written Danish. English also often uses a comma before a clause like this in some contexts, but Danish comma rules are its own system and learners should get used to seeing commas before subordinate clauses.

Yes. Siger is the present tense of at sige = to say.

• at sige = to say
• siger = says / is saying
• sagde = said
• har sagt = has said

So Læreren siger means The teacher says or sometimes The teacher is saying, depending on context.

Yes. Danish present tense often covers both the simple present and the present progressive meanings that English separates.

So Læreren siger can mean:

• The teacher says
• The teacher is saying

The exact meaning depends on context.

Yes, opførsel is a normal and common word for behavior, especially in contexts like school, manners, or conduct.

For example:

• god opførsel = good behavior
• dårlig opførsel = bad behavior

In this sentence, opførslen i klassen sounds very natural for behavior in class.

You could say:

En lærer siger, at en opførsel i en klasse er vigtig.

But that sounds unnatural in this context, because English and Danish normally talk about this idea with definite or more general wording. The original sentence sounds much more natural:

Læreren siger, at opførslen i klassen er vigtig.

It refers to a specific teacher and the behavior in that class situation.

A rough guide is:

• læreren ≈ LAIR-er-en

A few important points:

• æ sounds somewhat like the vowel in English air in many accents, though not exactly the same.
• The r sounds are Danish, so they may not match English r.
• In natural speech, unstressed syllables can sound weaker than you might expect.

If you want to sound more natural, focus especially on the first syllable lære-.

A rough guide is:

• opførslen ≈ OP-fur-slen or OP-fœr-slen

A few notes:

• ø is a vowel English does not really have, so learners usually need practice with it.
• The ending -slen may sound more compressed in natural Danish than it looks in writing.
• Danish pronunciation is often less clearly syllable-by-syllable than English learners expect.

It is a good word to learn by listening rather than relying only on spelling.

Yes, but the word order changes according to Danish grammar.

For example, if you put i klassen first in the subordinate clause, you would normally still keep the verb after the subject:

• Læreren siger, at opførslen i klassen er vigtig.

If you change the main clause, V2 applies:

• I dag siger læreren, at opførslen i klassen er vigtig.

Here siger stays in second position in the main clause because Danish main clauses follow the V2 rule.

So word order is flexible, but not random.