ابني في المدرسة.

Word by word, it is:

• ابني = my son
• في = in / at
• المدرسة = the school

So the sentence is literally My son is in the school, but in natural English it is often translated as My son is at school.

The base word is ابن = son.

When you add the suffix ـي, it means my:

• ابن = son
• ابني = my son

In this sentence, ابني is read as ibni in Egyptian Arabic.

A natural Egyptian pronunciation is:

ibni fil-madrasa

You may also think of it as:

ibni fi l-madrasa

In connected speech, في + ال often runs together, so fi l- sounds like fil-.

In Arabic, present-tense sentences like this usually do not use a word for is / am / are.

So:

• ابني في المدرسة = My son is at school

This is a complete sentence in Arabic even without a separate verb.

If you wanted the past, you would normally add a form of كان:

• ابني كان في المدرسة = My son was at school

It can mean either, depending on context.

• في often means in
• but with places, English may translate it as at

So ابني في المدرسة can be understood as:

• My son is in the school
• My son is at school

In everyday English, at school is usually the most natural translation.

That is a very common difference between Arabic and English.

Arabic often uses the definite article ال in places where English uses no article in an idiomatic expression. So:

• في المدرسة is literally in the school
• but the natural English meaning may be at school

So this is not strange Arabic grammar; it is just a different way the two languages package the idea.

The final ة is called taa marbuuTa. It often marks feminine nouns.

In this word, it is pronounced -a in normal Egyptian speech:

• مدرسة = madrasa

So المدرسة is pronounced il-madrasa or el-madrasa, depending on the speaker.

Because in fast speech, في connects closely to the following word.

• في = fi
• المدرسة = il-madrasa / el-madrasa

Together, they are often said as:

• fi l-madrasa
• or more smoothly fil-madrasa

Also, the ل of ال is pronounced here because م is a moon letter, so there is no assimilation.

For a negative sentence in Egyptian Arabic, you would usually use مش:

• ابني مش في المدرسة = My son is not at school

To turn it into a yes/no question, everyday Egyptian usually just uses intonation:

• ابني في المدرسة؟ = Is my son at school?

You may also see هل in more formal Arabic:

• هل ابني في المدرسة؟

But for spoken Egyptian, the plain sentence with question intonation is more natural.