If you see the message: Cannot share passages at this time, try again later
This is an error that Google Drive encounters sometimes if you are signed into multiple Google accounts at once. Please be sure that you are signed into both Chrome and Drive with the email address used to register for Fluency Tutor for Google.
If that doesn't solve the issue, the passages should already be in your Google Drive.
Navigate to the Fluency Tutor folder in your Google Drive, and open the subfolder for the date that you shared the passage, (i.e. 24 July 2014 11:35). From there you can use the standard method of sharing files in Google Drive with your students.
Students must also have Fluency Tutor for Google (Student App) installed. It can be installed by going to fluency.texthelp.com.