Wanafunzi waliochelewa walikosa maelezo muhimu darasani.

Yes:

• Wanafunzi = students
• waliochelewa = who were late
• walikosa = they missed / they failed to get
• maelezo = explanations / details / information
• muhimu = important
• darasani = in class / in the classroom

So the structure is basically:

Students who were late missed important explanations in class.

Wanafunzi is the plural form of mwanafunzi.

This is a Class 1/2 noun pair, which is very common for words referring to people:

• mwanafunzi = student
• wanafunzi = students

The change from m- to wa- is the noun-class change from singular to plural.

Because wanafunzi is plural and refers to people, other words in the sentence also use plural human agreement, such as:

• wa-li-o-chelewa
• wa-li-kosa

It is made of several parts:

• wa- = they / plural human subject agreement
• -li- = past tense
• -o- = relative marker here, giving the meaning who
• -chelew- = root meaning be late
• -a = final vowel

So:

wa-li-o-chelewa
= they-past-who-be late
= who were late

This is a very common Swahili pattern for relative clauses.

Because both refer to the same subject: wanafunzi = the students.

In both words:

• wa- shows a plural human subject
• -li- shows past tense

But after that, the two forms do different jobs:

• waliochelewa = who were late
  This is a relative verb form, so it includes the relative marker -o-.
• walikosa = they missed
  This is the main verb of the sentence, so it does not have the relative marker.

Compare:

• walichelewa = they were late
• waliochelewa = who were late
• walikosa = they missed

The verb -kosa can mean things like:

• miss
• fail to get
• lack
• not manage to obtain

In this sentence, walikosa maelezo muhimu means the students did not get or hear the important explanations because they were late.

So in natural English, missed is the best translation here.

Maelezo is usually treated as a plural noun in Swahili. It can mean:

• explanations
• details
• information

Its singular form is elezo, but in everyday use maelezo is much more common.

This can feel a little different from English, because English often uses uncountable words like information, while Swahili may use maelezo, which looks plural.

So maelezo muhimu can be understood as:

• important explanations
• important details
• important information

depending on context.

Because muhimu is usually an invariable adjective in modern Swahili.

Many adjectives change to agree with the noun class, for example:

• mtoto mzuri
• watoto wazuri

But muhimu normally stays the same:

• jambo muhimu
• mambo muhimu
• maelezo muhimu
• sababu muhimu

So even though maelezo is plural, muhimu does not change.

Darasani comes from darasa = class / classroom plus the locative ending -ni.

So:

• darasa = classroom / class
• darasani = in the classroom / in class

The suffix -ni often adds a location meaning such as:

• in
• at
• to

So darasani is a very natural way to say in class or in the classroom.

Yes. This sentence follows very normal Swahili patterns:

• Noun + relative clause
  wanafunzi waliochelewa = students who were late

• Verb + object
  walikosa maelezo = they missed explanations

• Noun + adjective
  maelezo muhimu = important explanations

• Location often comes near the end
  darasani = in class

So the sentence is built very naturally.

Swahili does not have articles like a, an, and the.

That means a noun like wanafunzi can mean:

• students
• the students

The context tells you which English translation sounds right.

In this sentence, English usually uses the students who were late, because the relative clause who were late identifies a specific group.

You would say:

Mwanafunzi aliyechelewa alikosa maelezo muhimu darasani.

Changes:

• wanafunzi → mwanafunzi
• waliochelewa → aliyechelewa
• walikosa → alikosa

So the agreement changes from plural human to singular human:

• plural: wa-
• singular: a-

And the relative form changes accordingly:

• waliochelewa = who were late
• aliyechelewa = who was late

Yes, depending on context.

The verb -chelewa often means:

• to be late
• to arrive late
• to delay / be delayed

In this sentence, waliochelewa naturally means the ones who were late or the ones who arrived late. Both ideas fit the situation.

English usually just says who were late.