Adverbial phrases without 'the' - such as 'at home' 'at work' 'in prison' - are fixed phrases referring to where person "belongs" or is registered - their own home, or the place where they're listed as a student, employee, resident or inmate. In BrE (but not in AmE) we also say 'in hospital' for a registered in-patient who's been admitted onto a hospital ward. This is different from at/in when used with an article - for example, 'at a school' or 'in the prison'. These phrases simply describe the location of a person or thing. Here's an explanation from a BrE perspective: 1. "At school" This can have one of two meanings: i. It can mean that the person is in full-time education. For example, "My older sister's a doctor; my younger sister is only 14, so she's still at school". ii. It can mean that the student (or teacher) is inside their own school building at the moment, attending lessons or teaching. For example: "Hi, is Amy there, please?" "No, sorry. Amy's at school at the moment. She'll be home at 4 o'clock." 2. "In school" This can have a similar meaning to 'at school'. I believe that "Amy is in school" is used in AmE for the first meaning i.e. a person still in full-time education. Note that AmE also refers to college and university as 'school', whereas BrE does not - in BrE, you only usually go to 'school' up to the age of 16 or 18. BrE speakers don't refer to higher education as 'school'. 3/4 "at the school" and "in the school" These refer to the physical location of a person (or object). In the case of a person, we'd understand that the individual wasn't a registered student or employee there. For example, "The fire brigade are at the school dealing with a fire in the science lab". "In the school" is similar, but with more of an emphasis on the physical interior of the building. For example, "When the tsunami hit the town, everyone sheltered in the school". In these cases, we know which school we're referring to. I hope that's clear.

Hi!! Well, we'd only use "the" with school if you are referring to a specific school that maybe you have named before in the conversation. The difference between "at" school and "in" school depends on the situation. At school means the person is literally, physically, inside the school. In school means the person is studying in general (usually at college or university) but not necessarily inside the school building at that moment. I hope this helps!

The thing about schools is that it is a location made up of more than one classrooms, so we can say at school, in the classroom. It is like at the shopping centre, inside the shopping centre or inside the shop. So the shift from at to in depends on the situation.