To identify which version of Google Sites you're using simply enter sites.google.com into your browser's address bar then look in the bottom-left corner of the screen. If the bottom-left corner of the screen has a "back to Classic Sites" button then you're using the current version of Google Sites. Here's a little video demonstration of those steps.
This post originally appeared on FreeTech4Teachers.com. If you see it elsewhere, it has been used without permission. Sites that regularly steal my (Richard Byrne's) work include CloudComputin, TodayHeadline, and 711Web.