学生在学校上学是 The students are at school.
那 The teacher is at school 对吗？还是应说成 The teacher is at the school?
可以说 The teacher is at school 的。
▲依据朗文词典，at school 有两个意思：
in the school building 在学校里
I can get some work done while the kids are at school. 孩子上学将来我可以干一些活。
[BrE] attending a school, rather than being at college or university or having a job 在求学，在上学（指中、小学）
Weve got two children at school, and one at university. 大家有两个孩子在读中学，一个在读大学。
▲依据 at school 的第一个意思（in the school building 在学校里），完全可以说 The teacher is at school。下面是两个来自原版词典的例子：
The teachers at schoolwere horrid.
My teachers at schoolgave me every possible encouragement.
