Ⅰ. at school表示“在学校、在上学”相对于在家里或在校外。如：
① My son is at school now. He is not at home or somewhere else. 我儿子现在在学校，他不在家，也不在别的地方。
② When my brother was at school, he studied very hard. 在学校时，我兄弟学习很用功。
Ⅱ. in school “在求学、在上学”相对于有工作。如：
My daughter still in school She doesn’t work.。 我女儿还在上学，她不在工作。
：①和②用at school 强调所在场所或时间。③中的in school 则强调主语的身份是学生。因此，in school. 和 at school的着重点不一样，通常不互换使用。
Ⅲ. In a / the school “在学校”，不一定指上学。类似的还有：
in hospital “生病住院”
in a / the hospital表“在医院”(工作或探视病人等)
at table “在吃饭”
at a / the table “在桌边”(有可能在聊天或看报)
① Is your friend in school? 你的朋友在上学吗?
① Your friend looked for you in the school just now. 刚才你的朋友在学校里找你。
② Children are often in hospital when they are young. 孩子们小的时候经常生病住院。
③ She is a good doctor in the hospital .她是医院里的一名好大夫。
When TV programs report wars or disasters, the editors rarely 阅读理解答案
Scientific experiments can sometimes go wrong and when they 阅读理解答案
Want a glance of the future of health care? Take a look阅读理解答案
美文赏析:整个世界因你而不同
You can never imagine how big and complex the inner world 阅读理解答案
看一场演唱会 Watch a Concert
《我们在一起》或将成为NBC的一部大热剧
新研究：世界最健康的5种饮食方式
电话不能取代书信 Phones Will Not Kill Letter Writing
One of my father’s favorite sayings as I was growing up阅读理解答案
《幻友玛丽》惨遭删减
表面之下 Under the Surface
金融英语之银行的种类
外事接待英语之约会
三个月拿下考研英语实战
For the last 10 years, job listing site CareerBuilder has put阅读理解答案
大学生炒股的英语作文College Students,out of Stock Market,Ple
Have you ever been out on a boat and felt it lifted up 阅读理解答案
房地产英语之洽租商铺 Retail Shop
These days I realize one thing which amazes me so much阅读理解答案