"Often they begin to get cold feet, and have second thoughts and doubts about whether they want to go," says Brian Harrison Jennings, general secretary of the Association of Educational Psychologists. "It's partly fear - a matter of whether they're going to be up to the academic challenge and to living on their own - that makes them question what they're about to do."
At this point they often start to talk about gap years, putting off university and perhaps getting a job near to home to stave off the decision. Parents should treat such anxiety for what it is and should only worry if their son or daughter suffers sleeplessness and an unusual amount of anxiety.
"Most adolescents feel fairly confident with what they know at the moment," says Mr Harrison Jennings. "They're conscious both of their powers and ability on the one hand, and their lack of knowledge on the other. They'll be going from having been a kingpin at their school, top of the academic and age ladder, to once again, for the fourth time in their 18 years, being the youngest and least important."
When they actually are at university, most students manage to adjust to life in the world, even if they are homesick at first. But a few don't. They may find it so difficult to handle that they leave in their first term. It's probably the right decision for them - they've had the guts to tell you they're not ready for it yet - and it could give them the time to develop the confidence they lack, say the experts.
Universities are usually very sympathetic and will hold a place open for a year. Consult tutors and pastoral care staff about this. No one should feel any shame about taking time out. Yes, it will mean they're a year behind their peers, but a year out at this age will not make very much difference, and might be an advantage.
The important thing is to fill the intervening year with something meaningful. Mr Harrison Jennings says: "It has to be something more than getting out of bed at two in the afternoon and dossing around watching telly all day." A job in a supermarket is fine as it involves youngsters meeting people, managing their time and surviving in the real world.
But the evidence shows that the vast majority of youngsters are up to it by the age of 18 and parents' fears are groundless.