Forum:Sending teenagers friends to college

How do you bring teenagers into the game to enable them to attend college? The Sims I send to college always want their friends to attend college as well but I don't know how to get them into the game to send them. A few are on the 'Send Sims to College' list but many are not. My Sim teenagers are always bring home friends who, I think, come from the Vacation pack. When they call them on the phone, the only options are 'Invite as houseguest (3 days)' or talk. Can anyone help with this? Thank you.