For all the people wondering about what constitutes a "school-issued email address" (.edu, .net, .ch, .ac.il, &c), we use the swot gem (https://github.com/leereilly/swot) to automatically identify domains belonging to academic institutions. You can see for yourself what's allowed, even send Pull Requests to include your school if it's missing. Anything that's not automatically accepted still goes through a manual review process.
And as others (johndbritton, jbarnette, jeremymcanally) have pointed out, you can contact us at support@github.com if you're having any trouble.
