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)