I just purchased an iPhone 4S and I am using iOS 5.1.1. Only one of my Google calendars is syncing. I've searched the web and have tried every suggestion, nothing is solving the problem.
You'll need to make sure that your account is properly configured in Settings > Mail, Contacts, and Calendars.
Since you're using Gmail, make sure that Calendars are set to ON and then go to the Calendar app and make sure all the calendars are selected to be displayed by tapping "Calendars" in the top left corner and checking off all the calendars you want to see from your Gmail account.
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That's the google recommended way http://support.google.com/mobile/bin/answer.py?hl=en&answer=139206
Maybe you have only enabled CalDAV syncing for the one calendar that works?
On this page you can select which calendars are to be synchronized to the CalDAV devices*: https://www.google.com/calendar/syncselect
*) iPhone etc.