As a native speaker of U.S. English, I would always say "at" (not in).

Google "he was a student at" (include the quotation marks) for many examples of this usage.

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Note added at 19 mins (2011-04-11 21:26:20 GMT)
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Here are some examples of how to use "at" and "in" correctly:

Use "at" when giving the name of a specific school/university.

Example: He is a student at Cambridge University.

Example: When Jane was a student at Princeton University, she had many friends.

Use "in" when naming a town/city/state/country:

Example: He studied in California for several years.

Example: We have been studying in Canada for two months now.

Use "in" when talking about a specific course/class:

Example: He sat next to me in my anthropology course.

Example: Susan is a student in Mrs. Brown's second grade class.


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Note added at 21 mins (2011-04-11 21:28:42 GMT)
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By the way, this should be an English/English question since there is no Arabic involved.