Magistra discipulos monet ut verba nova in sententiis suis experiantur.

Discipulos is the direct object of monet. With moneo, Latin often puts the person being warned, reminded, or advised in the accusative.

So the structure is:

• magistra = the teacher
• discipulos = the students
• monet = warns/advises

In other words, the teacher advises the students.

After verbs of urging, advising, warning, persuading, and commanding, Latin often uses ut + subjunctive to express what someone is being told or urged to do.

So:

• monet ut... = advises/warns [someone] to...

This is often called an indirect command or substantive clause of command.

Because it is inside the ut-clause after monet. In this construction, Latin requires the subjunctive.

So:

• monet = the main verb
• ut ... experiantur = the content of the advice/urging

A literal sense is: The teacher advises the students that they should try...

Experiantur is:

• present
• subjunctive
• third person plural

It comes from experior, experiri, expertus sum, meaning try or test.

So experiantur means they may try / they should try / let them try, depending on context. Here it works as that they try or to try in the indirect-command sense.

Because experior is a deponent verb.

A deponent verb:

• has passive-looking forms
• but an active meaning

So although experiantur looks like a passive form, it means they try, not they are tried.

Because nova is an adjective modifying verba, and adjectives in Latin must agree with the nouns they describe in:

• gender
• number
• case

Here:

• verba = neuter plural accusative
• nova = neuter plural accusative

Together they mean new words.

They are the object of experiantur.

In this sentence, the students are being advised to try new words, so new words is what they are trying out. That makes verba nova the direct object, so it appears in the accusative.

The preposition in takes the ablative when it means in, on, or within a place or setting.

Here it means in their own sentences, so:

• in
  • ablative
• sententiis = ablative plural
• suis = ablative plural, agreeing with sententiis

If in meant motion into something, it would usually take the accusative instead.

Suis is a reflexive possessive adjective, meaning their own. It refers back to the subject of its own clause.

In the ut-clause, the understood subject of experiantur is the students. So suis refers to the students, not to the teacher.

That is why the phrase means in their own sentences.

Latin uses suus, sua, suum when the possessor is the subject of the clause.

Here, in the subordinate clause, the students are the understood subject of experiantur, so their own sentences is sententiis suis.

If Latin used eorum, it would sound more like in their sentences referring to some other people, not reflexively back to the students themselves.

Latin word order is much more flexible than English word order. Very often, the verb comes near the end of the clause, especially in careful or literary Latin.

So Magistra discipulos monet ut verba nova in sententiis suis experiantur is perfectly normal Latin word order.

Putting experiantur at the end also lets the sentence build up to the main action of the ut-clause: that they try them out.