1) Make sure you are logged into your google apps account and are at the 'mail' screen. Click compose and start to type the names of students in the class in the 'to' field - you can use last names or first names - it should auto complete as the students are in the system, if the correct name pops up, click on it and move onto the next. When you have the complete list send the email - name it test, or just say hello. This is a funny way to do it, but with out sending them an email first, the boys will not be in your 'address book' - don't ask me why, its an admin issue?!
4) Your new group will now appear in all google apps, when you are sharing forms, documents or calendar invitations the group will show up when you start to type it (the name of the group) in the 'to' field of the application you are using.
To send mail to contact group;
1) Compose a message from your gmail apps account and in the 'to' field start writing the name of the group, all the names should appear - you can add and remove names from the list by highlighting and deleting them.
2) You can also send mail from within the contact manager by selecting a group, selecting which names you want to send to, and then clicking the envelope button!