What's the difference between "at" and "in" ?

[GabrielPaixão]

I want to know when can I use "at" and "in" ?
Example: At school / In school
What's the difference ?

Thanks.

[bhaisahab]

I want to know when can I use "at" and "in" ?
Example: At school / In school
What's the difference ?

Thanks.

In BrE we usually say "at school" to mean someone is a pupil/student at an educational establishment other than college or university.

[emsr2d2]

We use "at school" to explain that they are between the ages of 4 and 16 and are therefore in compulsory education at either a primary, a junior or a secondary school.
How many kids do you have at university?
None. My kids are 8, 11 and 14. They're all [still] at school.

We also say "at school" to give a pupil's location on an individual day.
Where's your daughter?
She's at school. She will be home at 4pm.

[billmcd]

Pardon me emsr2d2 for using your response as a way to identify the differences between BrE and AmE. We use "at school" to explain that they are between the ages of 4 and 16 and are therefore in compulsory education at either a primary, a junior or a secondary school. In AmE we would not use "at" in this way. We would typically use "in".
How many kids do you have at university? In AmE you would typically hear, "How many kids do you have 'in college'?", regardless of whether the institution is classified as a college or university.
None. My kids are 8, 11 and 14. They're all [still] at school. We would use "in".

We also say "at school" to give a pupil's location on an individual day. Same in AmE.
Where's your daughter?
She's at school. She will be home at 4pm.

b.