Where can I find info on computer to student ratio?

I am trying to compile information based on year for the average of computers to students in elementary schools nationwide. I am starting at 1990 and ending at 2010. The problem is, I'm not finding the information I need. Can anyone help to point me in the right direction? I really need to finish this project as I have more homework to finish up tonight. Your help is GREATLY appreciated! Thank you!