Running the most recent version of OS X Mountain Lion and iOS 6.0, I'm able to sync all my Reminders between all my devices.
However, though the Reminders themselves will sync across all my devices, their completion state will only cross the same platform (that is, if I complete a Reminder on OS X, all my Macs will show as complete, but not my iOS devices, and vice versa).
Is there a setting that I can check somewhere to fix this, or is it working as intended?
Best Answer
Quoting a solution I found in the Apple community web site:
Link here.