He works at school.
at school
a) in the school building: 在学校
I can get some work done while the kids are at school.
b) British English 英式英语,求学 attending a school, rather than being at college or university or having a job:
We've got two children at school, and one at university.
in school
a) in the school building: 在学校
Sandra's not in school today.
b) American English 美式英语,求学 attending a school or university rather than having a job:
Are your boys still in school?
参考资料:朗文当代英英辞典
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