الطالب اللي قاعد وراي بالقاعة ناسي دفتره.

اللي is the Levantine relative word meaning who / that / which. It introduces a clause that describes الطالب.

So:

الطالب اللي قاعد وراي بالقاعة
= the student who is sitting behind me in the classroom

In Levantine, اللي does not change for gender or number, so you use the same form with masculine, feminine, singular, and plural nouns.

Usually no, not with a definite noun like الطالب = the student.

So الطالب اللي... is the normal way to say the student who...

But with an indefinite noun, Levantine often drops the relative word:

طالب قاعد وراي بالقاعة
= a student sitting behind me in the classroom

So a useful contrast is:

• الطالب اللي قاعد... = the student who is sitting...
• طالب قاعد... = a student sitting...

Because they both describe الطالب, which is masculine singular.

• قاعد agrees with الطالب
• ناسي also agrees with الطالب

If the noun were feminine, you would normally say:

الطالبة اللي قاعدة وراي بالقاعة ناسية دفترها

So this is normal agreement:

• masculine singular: قاعد، ناسي
• feminine singular: قاعدة، ناسية

Here, قاعد most naturally means sitting.

So قاعد وراي is literally sitting behind me.

In Levantine, قاعد can also be used more broadly in some contexts, sometimes almost like staying or even as part of a progressive meaning. But in this sentence, because it is followed by a location phrase, the plain physical meaning sitting is the most straightforward reading.

In Arabic, the present tense often does not use an expressed verb to be.

So where English says:

The student ... is forgetful / is sitting

Arabic can simply say:

• قاعد = sitting
• ناسي = forgetful / having forgotten

There is no separate present-tense is needed.

That is why ناسي دفتره works by itself as the predicate: he has forgotten his notebook / he forgot his notebook and still does not have it

Both words have attached pronoun endings.

• ورا = behind
• وراي = behind me

Here, -ي means my / me

And:

• دفتر = notebook
• دفتره = his notebook

Here, -ه means his

This kind of attachment is very common in Arabic:

• وراك = behind you
• وراه = behind him
• دفترها = her notebook

In actual Levantine pronunciation, دفتره is often said more like daftaro.

بالقاعة is made of:

• بـ = in / at
• القاعة = the hall / the classroom / the lecture hall

So بالقاعة means in the classroom, in the lecture hall, or in the hall, depending on context.

Also notice that بـ + ال becomes بالـ in writing and speech.

ناسي is an active participle, and in Levantine active participles are often used to describe a current state resulting from an action.

So:

• نسي دفتره = he forgot his notebook
• ناسي دفتره = he has forgotten his notebook / he’s forgotten his notebook

The second one focuses more on the present result: right now, he does not have the notebook with him.

This is extremely common in spoken Arabic.

A helpful way to break it up is:

• الطالب = the student
• اللي قاعد وراي بالقاعة = who is sitting behind me in the classroom
• ناسي دفتره = has forgotten his notebook

So the whole sentence is built like this:

[noun] + [relative clause describing the noun] + [main comment about that noun]

In other words:

The student who is sitting behind me in the classroom
has forgotten his notebook

The subject is a long noun phrase, and ناسي دفتره is what is being said about that subject.