Re: What's the difference between "at" and "in" ?
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.
Remember - correct capitalisation, punctuation and spacing make posts much easier to read.