Bona disciplina magnum commodum discipulis dat.

Because bona is describing disciplina, and Latin adjectives must agree with the nouns they modify in gender, number, and case.

• disciplina is feminine, singular, nominative
• so the adjective must also be feminine, singular, nominative
• the feminine nominative singular form of bonus, -a, -um is bona

So bona disciplina means good discipline.

You know from both its case and the verb ending.

• disciplina is in the nominative singular, which is the case usually used for the subject
• dat means he/she/it gives, so the verb is 3rd person singular
• disciplina matches that singular verb

So disciplina is the thing doing the action: good discipline gives.

Because it is the direct object of dat.

The verb dare means to give, and what is being given here is magnum commodum:

• commodum = benefit / advantage
• magnum = great / large

Since it is the thing being given, it goes in the accusative case.

Both words are accusative singular because:

• commodum is neuter singular accusative
• magnum agrees with commodum

Because it is the indirect object: the people to whom something is given.

With verbs like do, dare (to give), Latin commonly uses:

• accusative for the thing given
• dative for the recipient

So:

• magnum commodum = the thing given
• discipulis = to the students

That is why discipulis is dative plural.

Because the subject is singular.

• disciplina = singular
• dat = gives (3rd person singular)
• dant would mean they give and would need a plural subject

So bona disciplina dat means good discipline gives, not good discipline give or good disciplines give.

It comes from the verb do, dare, dedi, datum, meaning to give.

Here dat is:

• present tense
• active voice
• indicative mood
• 3rd person singular

So it means he/she/it gives.

Because the subject is disciplina, the natural translation is it gives or simply gives.

Because Classical Latin has no articles.

English says:

• the discipline
• a benefit
• the students

Latin usually just says:

• disciplina
• commodum
• discipulis

The exact sense—a, an, the, or sometimes no article at all—has to be understood from context.

Because Latin word order is much more flexible than English word order.

English relies heavily on position:

• Good discipline gives a great benefit to the students

Latin relies more on endings:

• disciplina is nominative, so it is the subject
• commodum is accusative, so it is the direct object
• discipulis is dative, so it is the indirect object

That means Latin can move words around for style, emphasis, or rhythm without changing the basic meaning.

For example, these would still mean essentially the same thing:

• Bona disciplina magnum commodum discipulis dat
• Disciplina bona discipulis magnum commodum dat
• Magnum commodum bona disciplina discipulis dat

Because magnum is an adjective modifying commodum, and both are:

• neuter
• singular
• accusative

Latin adjectives must match the noun they describe. So:

• commodum = neuter accusative singular
• magnum = neuter accusative singular to agree with it

This is the same agreement pattern you saw in bona disciplina, just with a different gender and case.

Not always. Latin disciplina can have a wider meaning than English discipline.

Depending on context, it can mean things like:

• instruction
• training
• education
• discipline

So a learner may need to be careful not to assume only the narrow modern English meaning. In this sentence, the intended meaning is already given, but it is useful to know that the Latin word can be broader.

Commodum often means benefit, advantage, or convenience.

In this sentence, magnum commodum means something like:

• a great benefit
• a great advantage

It is a neuter noun, and here it is the thing being given.

Yes. That is a very natural translation.

Latin uses:

• discipulis = to the students
• but English often prefers the students as an indirect object without to

So both of these are good English translations:

• Good discipline gives a great benefit to the students
• Good discipline gives the students a great advantage

The Latin grammar is the same either way.