Magistra dicit responsum eius verum esse.

A quick breakdown:

• magistra = the teacher; nominative singular, so it is the subject of dicit
• dicit = says; 3rd person singular present
• responsum = answer; accusative singular
• eius = his / her / its; genitive singular, modifying responsum
• verum = true; accusative singular neuter, agreeing with responsum
• esse = to be

The main clause is:

• Magistra dicit = The teacher says

Then the rest, responsum eius verum esse, is what she says.

This is a very common Latin pattern called an indirect statement.

Because after verbs like dicit (says), Latin often uses an indirect statement construction.

In English, we usually say:

• The teacher says that his/her answer is true.

In Latin, instead of using a word like that plus a normal finite verb (est), Latin usually uses:

• accusative + infinitive

So:

• direct statement: Responsum eius verum est = His/her answer is true
• indirect statement after dicit: Magistra dicit responsum eius verum esse = The teacher says that his/her answer is true

So esse appears because Latin is turning the statement into reported speech.

In an English-style sentence, you would expect the subject of to be to stay in the nominative. But in Latin indirect statement, the subject of the infinitive goes into the accusative.

That is the key rule.

So in:

• responsum eius verum esse

the word responsum is logically the subject of esse, but grammatically it is accusative because it is the subject of an infinitive in indirect statement.

This is often called the accusative-and-infinitive construction, or AcI.

Because verum agrees with responsum.

Here, verum is a predicate adjective, meaning it describes responsum after esse:

• responsum ... verum esse = the answer to be true

Since responsum is:

• accusative
• singular
• neuter

verum must match it:

• accusative
• singular
• neuter

That is why it is verum, not verus or vera.

This is a very common learner question.

• eius means his / her / its and is non-reflexive
• suus, sua, suum is reflexive, and usually refers back to the subject of the main clause

So in this sentence, magistra is the subject of dicit. If Latin used suum, it would normally point back to magistra:

• Magistra dicit responsum suum verum esse
  = The teacher says that her own answer is true

But with eius, the answer belongs to someone else, not to the teacher herself.

So eius tells you that the answer is his/hers, but not the teacher’s own.

By itself, eius can mean:

• his
• her
• its

Latin does not show the gender of the possessor in this form. You figure it out from context.

So this sentence alone does not tell you whether the answer belongs to a male person, a female person, or possibly a thing. The surrounding context would decide that.

Because Latin usually does not need one in this kind of sentence.

English says:

• The teacher says that the answer is true

Latin normally expresses this idea through the accusative + infinitive construction instead of using a separate word for that.

So:

• English: says that ... is ...
• Latin: dicit ... esse

That is just how reported statements are usually built in Latin.

Yes, the word order can be different.

Latin word order is much more flexible than English word order because the endings show the grammatical relationships.

So all of these are possible in principle:

• Magistra dicit responsum eius verum esse
• Magistra responsum eius verum esse dicit
• Responsum eius verum esse magistra dicit

The version you have is perfectly normal. Putting esse at the end is especially common in Latin.

So the order helps with emphasis and style, but the endings are what tell you the grammar.

Because responsum is a neuter second-declension noun.

That is why its singular nominative and accusative are both responsum.

This matters here because:

• the noun is neuter
• the adjective modifying it or agreeing with it must also be neuter

So the sentence has:

• responsum
• verum

both in neuter singular.

For an English speaker, this can feel unusual because English nouns do not have grammatical gender in the same way. But in Latin, the noun’s gender is a basic part of how agreement works.

The direct statement would be:

• Responsum eius verum est.

That means:

• His/her answer is true.

When Latin turns that into reported speech after dicit, it changes:

• est → esse
• the subject responsum → accusative responsum
  (for this neuter noun, nominative and accusative happen to look the same)

So:

• direct: Responsum eius verum est
• indirect: Magistra dicit responsum eius verum esse

Seeing both side by side is often the easiest way to understand the construction.