b.Is it true that in American English, in school is more common whereas British English favours at school? I would not consider it more common. Somehow, I can't bring myself to use the former unless I feel the need to emphasize the person is in the building. Agree. Would an American find it funny if they read or heard the sentence, "She is at school"? No, that would be a common response to "Where is Maria?"
Student or Learner