Student or Learner
How should I know where to use at school and where in the school?
The children are at school today. (physically present)
There are 546 pupils in the school. (registered as students)
Is your daughter still in school? (This means, 'Does your daughter still attend school, or has she graduated?')
Is your daughter still at school? (This means 'Has your daughter returned home from school yet today?) (Depending on the context, it can mean the same as 'in school'. This is a question of personal/regional usage, I believe.)
I hope this is helpful,