I checkmarked the option to require users to read a guide when changes are made to it, so far it doesn't seem like it's working.

How should it work, will it display the first time they access the site regardless of what URL they are using to get to the site.

It will display the first time they view the site after it's been set to required reading. Modifications to a guide will not trigger the requirement again. You would have to undo making it required, then refresh that requirement again. Doing so should delete all the history of anyone having viewed the page.

I had someone test it, and it wasn't working that way.

Odd. I'll have a look to see what's up. Nothing's changed in that code, so I'm not sure why it wouldn't be working anymore