Transitions are always hard. The one from teen to adult is probably the hardest, for both parent and teen. You want it all to go well, but you can't do it for your teen. Their stress in leaving is enormous, whether they want to go or not. You can help them most by active listening, asking their permission to comment after they have calmed down, offering suggestions, but letting them make their own choices. Be there for them emotionally and let them fly.