Passing a variable from one page to another.

I am creating a photo ID web application that will be able to look up students by their ID number. Once you have the student pulled up you have an option to create a temp id. I have the id as a public variable so when the temp id button is hit it opens a new window uses that variable to pull the data and create the temp ID. My problem is because it is a variable stored on the server when multiple people are using the application sometimes the id person 1 looked up shows up when person 2 tries to create the temp id instead of the id person 2 was using. Any ideas how I can correct this? I tried a converting the id into a hidden  field but could not get it to pass to the other page. I am using Visual Studios 2010 asp.net vb.net.
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