Thanks Jamie,
A drive is identified by the DriveID, it is unique for every blood drive we host.
I'm actually not sure why the report is grouped on account internal name, I am modifying an report designed before me. But to answer your question, the internal name relates only to the account.
DriveMaster.AccountID links to Accounts.AccountID and Accounts.InternalName is a user friendly name (Wal-Mart, Home Depot, etc...) for the account. So an account can host multiple drives, but each drive will only have one host.
Hope that makes sense.
But I followed your advice and removed the group on Internal Name, placed my FromDateTime field in the group footer for Accounts.AccountID and the MAX group in the group footer for Drive ID. And it seems to be working great now.
Thanks again!