HTC EVO Does Not Sync Google Calendar
I'd make sure that he's done something with Calendar through the web interface, such as add a custom calendar, and then try to add the account to the phone again. To do this you need to clear the data for all Google apps -- Accounts and Sync, Gmail, Google Framework Services, etc. -- and then re-add the account.

I don't believe this is EVO-specific, it seems sometimes Google just doesn't correctly link the accounts sometimes (for example, this question has the same problem except for Picasa: Why can&#39;t I Sync Picasa Web Albums?).