How do American English and British English use the definite article differently?

I decided to make sure that I know this important difference between American and British English, so I wrote what I have found out so far and I would be grateful to anyone who reads this and tells me whether I am wrong, or not.

In British English when people say to hospital or in hospital when talking about somebody being there as a patient they don't use the definite article : "I had to go to hospital", "She spent two weeks in hospital". And the meaning is that somebody was there as a patient.

If then for some other reasons British English speakers will use the definite article which will change the meaning itself, I noticed that, in American English, native speakers often use the the and if they need to show that somebody is in church to pray, in school as a student, in hospital as a patient, in prison as a prisoner, they use 'in' and not 'at'. Do American English speakers use 'at' like British English speakers use 'the' to give the sentences a different meaning?

Are my sentences correct? Do they show American English usage?

• He is in the school. (enrolled as a student)

• He is at the school. (for some different reasons)

• He is in the hospital. (as a patient)

• He is at the hospital. (visiting somebody)

• He is in the church. (to pray)

• He is at the church. (for some different reasons)

• He is in the university. (as a student)

• He is at the university. (not as a student)

• He is in the college. (as a student)

• He is at the college. (Not as a student)

• He is in the prison. (as a prisoner)

• He is at the prison. (not as a prisoner)

AmEng speakers do NOT use definite articles all the time; whether we do or not depends on what we want to say, and how we want to sound saying it. In particular, the use of the definite article with the present tense of the verb "to be" depends (in the words of a famous American) on what your definition of "is" is. Several of your example sentences sound distinctly unnatural to my USAite ear. Here are my suggestions based on my own usage:

School:

• He is in school. - He is a student; specific time does not matter. Perhaps it's Friday night and he's partying right now.
• He is in the school. - This does not sound natural at all to an American ear.
• He is enrolled in the school. - He is a student.
• He is at school. - He might be a student OR a teacher, but he is on the premises at this moment.
• He is at the school. - "The school" is a local landmark, and he's there right now.

Hospital:

• He is in hospital. - He's an inpatient. This is valid, but not usual American usage. Anglophiles (Americans who like to drop Briticisms into their speech to appear more sophisticated) will sometimes use this.

• He is in the hospital. - He's an inpatient.

• He is at hospital. - We don't say this.

• He is at the hospital. - He might be an outpatient, or he might work there; either way, he's there right now.

Church:

• He is in church. - Services are in progress right now, and he's there.

• He is at church. - Interchangeable with "in church".

• He is in the church. - He's inside the building; no information is conveyed about what he's doing there (he might be polishing the floor, for example.)

• He is at the church. - He's on the church grounds, not necessarily inside the sanctuary.

University/ College:

• He is in university. - Americans don't usually say "in university"; "in college", however, means that he's a student.

• He is enrolled in university. - He's a student.

• He is at university. - He's a student. This is much more common than "in university", for some reason.

• He is in the university. - Again, we don't say this.

• He is at the university. - The university is a local landmark and he's there now. (Who is he - student, professor, tourist? Not enough information.)

Prison:

• He is in prison. - He's a prisoner.

• He is at prison. - We don't say this.

• He is in the prison. - He's inside the building. He might be a prisoner, a warden, a visitor...

• He is at the prison. - He's on the grounds, not necessarily inside the building - he might be waiting in the car while his wife visits her brother.

In AmE, for your examples:

• No. He is in school. (enrolled as a student)

• Yes. He is at the school. (for some different reasons)

• Yes. He is in the hospital. (as a patient)

• Yes. He is at the hospital. (visiting somebody) or could be a patient, too.

• No. He is in church. (to pray)

• Yes. He is at the church. (for some different reasons)

• No. He is at/attending college. (as a student)

• Yes. He is at the university. (not as a student)

• No. He is in/at college. (as a student)

• Yes. He is at the college. (not as a student, the physical place)

• No. He is in prison. (as a prisoner)

• No. He is in the prison. (not as a prisoner)

The general rule is 'in X' for being part of the institution, but 'at the X' or 'in the X' for being physically related to the building (but note that this doesn't always work: 'in the hospital'). And the institution is 'in college' even if it is nominally a university.

I am a native English speaker in the U.S. This is how I would word your sentences:

He is in the school. (Enrolled as a student) — He is in school.

He is at the school.(For some different reasons) — Okay as worded.

He is in the hospital. (As a patient) — Okay as worded.

He is at the hospital. (Visiting somebody) — Okay as worded.

He is in the church. (To pray) Can also say, "He is in church."

He is at the church. (For some different reasons) Can also say, "He is at church."

He is in the university (As a student). He is at the university.

He is at the university. (Not as a student) — Okay as worded. You would need to add other words to make it clear if he is a student or just a visitor.

He is in the college. (As a student) — He is in college.

He is at the college. (Not as a student) — Okay as worded.

He is in the prison. (As a prisoner) — He is in prison.

He is at the prison. (Not as a prisoner) — Okay as worded.

I'm an American and I don't claim to know much about British English, but I can discuss nuances of American usage, and you can compare to British.

This brings to mind the time when my wife got a job working at a prison. Her mother called, and I said, "Oh, didn't you know? She's in prison." Of course she wasn't really "in prison", she was just "in the prison" or "at the prison".

You are correct that we never say someone is "in hospital" or "at hospital". It's always "in the hospital" or "at the hospital". If you say that someone is "in the hospital", that would normally be taken to mean he was a patient, but not necessarily. An American might also say someone was "in" to distinguish from "out", or one building from another. Like, "I was waiting for you at the pharmacy, but when you didn't show up I went in the hospital to look there." "At the hospital" almost always means not as a patient. Like, "I was at the hospital visiting grandma" or "I was at the hospital deliverying the mail".

With school the usage changes ... for no reason apparent to me. We say a student is "in school". That can either mean that he is in the school building at this moment, like, "Where is Bob?" "He's in school". Or it can mean that he is enrolled as a student, whether he is presently in the building or not. Like, "Does your daughter have a job yet?" "No, she's still in school." It could be night-time or a weekend so she's not actually in the school building at the moment, but she is still a student. "At school" is usually used to refer to a student who is enrolled and is on campus at this moment. "In the school" would mean in the building, whether as a student or a teacher or visiting. "At the school" usually means a non-student who is in the building or on campus. Just to make things complicated, a student who lives at school part of the year -- a boarding school or college -- can be said to be "at school" during the period that they are there rather than at home. So you might say "Sally is at school" when it is the time of year when she is residing in the town where the school is located, even if she is not actually on campus at that moment.

Whew, I didn't realize this was so complicated until you asked!

College and university work the same as school.

Church is different, probably because people don't "enroll" in church. (I suppose you could say that being a member of the church is the same idea. Whatever.) "In church" generally means in the building to worship or participate in some church activity. "In the church", "at church", and "at the church" would all normally be understood to mean physically in the building, but not necessarily to worship. "In" would normally be understood to mean literally in the buildling, while "at" and "at the" could mean in the building or generally on the grounds. Like if someone is there playing on the church softball team, we'd generally say they're "at the church" rather than "in the church".

He is in the hospital. (as a patient)

He is at the hospital. (visiting somebody)

A point about this. This seems to be correct for American English.

From my British perspective, these are sentences for referring to a particular hospital. Someone might say these when it is clear from the context of a conversation, that they are referring to a particular hospital.

In the general sense, the word "the", would not be necessary. For example, if you talk about someone who was taken to a hospital but, you don't need to specify which one in particular; you could say "He is in hospital." (as a patient). This is the normal way to say it, in the UK.