PHP - Sessions not being saved across pages

PHP - Sessions not being saved across pages

I know there are a million questions like this, but I've tried everything
I could find.
I call session start at the very top of every page I have. I've got no
session_destroy() calls either.
I'm on a default installation of xampp on Windows 7.
I did make sure that PHP had permission in the session tmp directory, I
see session files being created with the id of the session, which I set to
print out at the top of every page. The session ID does remain constant
when I flip through pages, but it doesn't recognize the variable I set on
a different page.
Thanks for your time!