Discipulas eiusdem vitii taedet: semper enim festinant et ideo errant.

Because taedet is one of a small group of Latin impersonal verbs. With taedet, the person who feels the emotion goes into the accusative, not the nominative.

So in:

Discipulas eiusdem vitii taedet

discipulas means the schoolgirls / female students as the people affected, even though it is accusative.

A very literal way to think of the structure is:

It disgusts / wearies the schoolgirls of the same fault.

More natural English usually rearranges this idea, but the Latin grammar is built this way.

Because taedet normally takes the genitive for the thing that causes disgust, weariness, or annoyance.

So:

• discipulas = the people affected
• vitii = the thing they are tired of / disgusted by

This is a standard pattern with taedet and some related verbs such as miseret, pudet, piget, and paenitet.

Eiusdem is the genitive singular of idem, eadem, idem, meaning the same.

So eiusdem vitii means of the same fault or of the same vice.

A learner can easily confuse eiusdem with eius, but here it is not just the pronoun his/her/its. It is the full form meaning of the same.

Also, eiusdem agrees with vitii, not with discipulas:

• vitii = genitive singular neuter
• eiusdem = genitive singular, matching it

Because taedet is being used impersonally, and impersonal verbs are normally in the third person singular.

So Latin does not say taedent here. It uses singular taedet, even though more than one person is affected.

That is a normal feature of this verb, not a mistake.

The subject is understood as they, referring to the same girls, but now in the nominative.

So the sense is:

• Discipulas eiusdem vitii taedet = the girls are tired of the same fault
• semper enim festinant et ideo errant = for they always hurry and therefore make mistakes

Even though the same people are being talked about, the grammar changes from one clause to the next:

• with taedet, they appear in the accusative
• with festinant and errant, the understood subject is nominative discipulae or simply eae

Enim means for, indeed, or you see, depending on context. Here it introduces an explanation:

for they always hurry...

Latin enim is a postpositive word, which means it usually comes second in its clause, not first.

So:

• semper enim festinant

is normal Latin word order.

An English speaker may expect enim semper festinant, but that is not the usual placement.

Ideo means therefore, for that reason, or that is why.

It points back to what came before:

• semper enim festinant = they always hurry
• et ideo errant = and therefore they make mistakes

So ideo marks the result of their hurrying.

Because the sentence is talking about one same fault that they all share, not several different faults.

So eiusdem vitii means:

• of the same fault
• not of the same faults

The singular suggests a single bad habit or recurring weakness, namely the one explained after the colon: they are always in a hurry.

The colon introduces an explanation of the fault just mentioned.

So the structure is:

• Discipulas eiusdem vitii taedet = the girls are tired of the same fault
• : semper enim festinant et ideo errant = namely, they always hurry and therefore make mistakes

In other words, the part after the colon explains what that same fault is.

Yes. Latin word order is flexible, and the first clause is arranged in a very Latin way:

Discipulas eiusdem vitii taedet

A learner might expect something more mechanically arranged, but Latin often places important words early and puts the verb at the end.

Here you can read it as:

• discipulas = the affected people
• eiusdem vitii = the thing they are tired of
• taedet = the impersonal verb that completes the idea

So the sentence is a good example of how Latin uses case endings more than fixed word order to show meaning.

It can mean either, depending on context. The basic idea of errare is to go astray.

In this sentence, because the idea is:

• they hurry
• and as a result they do something wrong

the natural sense is they make mistakes or they go wrong, rather than physically they wander around.

So context tells you which English wording fits best.