how I fixed my problem
I"m new here and got here by googling for help with my Android Tablet. I could not get the calendar to sync with my MAIN gmail account. Everything else related to that account would sync except for the calendar. My phone syncs fine. For some reason the main gmail account wasn't "visible" or something. My tablet didn't give me the option of setting the default account. In the settings it would show all of the accounts....just when I went to sync all....calendar would not sync for the main account.
I had added another gmail account for the entire family and somehow that calendar was visible and syncing. What I ended up doing was deleting that second "family" account from the tablet, restarted it and now my main gmail calendar is syncing fine. I have not yet attempted to re-add the second family account and probably won't do so. I have found a really nice app for the family: "Cozi" and they can all use their own email accounts.