Brid thought she had pretty much mastered the whole business of sending her children off to college. Then her 20-year-old son - the second in the family to go away to third level - more or less disappeared for a week at the start of second year.

"I asked him to ring us, to let us know if he'd got fixed up in a flat, and to let us have an address or phone number. He didn't ring, didn't come home on the Friday as planned, still didn't ring. I made myself stay calm, decided that if we hadn't heard by Monday morning, that I would telephone the college. And finally, he rang on Sunday night."

Her son's behaviour might seem outrageous to parents who've just graduated to having a child at third level, but Brid is philosophical. "They do forget to ring - unless of course they've run out of money."

Family life undergoes a major change when children go to college, a change just as profound as when they first started school 14 or so years before. But where starting primary school produced order, and a structure around which many families build their lives - it starts around 9 a.m., finishes around 2 or 3 p.m., and everyone knows where they're at - third level can have quite the opposite effect.

If children are living at home and commuting to college, it may be months (if ever) before their days take on a predictable pattern, so you're never sure if they'll be home for dinner or out in time for you to settle down to PM Live. If they've gone away, the routine may be predictable, but disruptive - they'll arrive home every Friday night with their laundry, expecting lots of TLC after a tough week in college until they return on Sunday night. You and your younger children may be surprised at how much you miss your college child at the evening meal, unprepared for how much quieter the house has become, and shocked at the mild resentment you feel about the disruption her new life creates in your old one.

You have TO expect change - but what sort of behaviour is it reasonable to expect? That they'll ring home if they're going to miss dinner? Stay out all night? Be three hours late coming home at the weekend? What should a parent do if it seems a child parties all night and regularly misses early lectures? Or is depressed and unhappy and home in time for dinner every night? Ann, a mother of six with two children in college, two who've finished and two still in secondary school, says: "You have to assume they'll go off the rails at first, that even the quietest of them will go mad; they suddenly have so much freedom."

That's a phase that could last for the first month or two of college at least, she reckons. She likes her children to let her know where they are, but doesn't get uptight about missed meals "especially now that most of us have microwaves".

Another Dublin mother with two daughters at local colleges agrees: where once she may have wanted a map of her children's movements, now she just says "ring me if you're not coming home". And after a few 3 a.m. calls, she's not even sure she wants to know that much any more.

In many ways, it probably is harder for parents whose children are still living at home to adjust to their new lifestyle. The important thing, says psychologist Marie Murray, co-author of the recently-published bestseller, The Teenage Years, is to approach the whole business with flexibility. "This is especially important in the early days, when the student is finding his or her way in an unpredictable world," she says. "There are social events, going out for coffee with new friends - it's unhelpful if parents ask them to establish a predictable pattern early on."

But it isn't unreasonable, she adds, to expect children to go to lectures, and it's probably a good idea for parents to know their child's schedule. And if they appear to be missing a lot of classes, it's not unreasonable for parents to remind students of their responsibilities - after all, even without fees, parents are usually funding their children to go to college.

The pattern is different if a child goes away to college. If they are still on the island of Ireland, then you might be surprised to discover that they'll be home every weekend. Thousands of college kids hop on the bus about noon every Friday to go home to their old life.

Both Ann and Brid agree that whether their students come home after a week or after a few months, they do more or less expect everything to stop for them. And although both mothers admit to mild feelings of resentment about this, they still cook favourite meals and make sure the laundry is all done in time for the return journey on Sunday night.

Both are sensitive to the fact that younger children can also resent the intrusion, and the fact that older brothers and sisters become a new centre of attention at the weekend.

Murray says children have to understand that this is all part of the give and take of family life. However, she warns, if there are Leaving Cert children in the family, make sure they still have the attention and support their older brother or sister had last year. It is very easy for parents to get caught up in the drama of their eldest child's life.

Although it's expensive to have a child away at college, there can be advantages: for one thing, you won't worry if they miss lectures and stay out late if you don't see it happening. Ironically, children may become more responsible and less likely to skip classes just because no one knows or cares whether they do or not.

"One study showed that going away to college helped to improve relations between parents and children, as well as developing a sense of responsibility," Murray says.

Money, of course, is a major issue, especially where children are living away from home. This is a good time for students to learn how to budget, Murray says - and parents shouldn't be in too much of a hurry to bail them out.

All families arrange things differently: Ann gives her living-at-home child an allowance of £350 per term to pay for everything from transport to food to social life, and expects her to budget it herself. Brid and her husband give their children a weekly allowance of about £35 to cover more or less the same (rents are paid separately).

However, Brid reckons that unless children is very responsible, they may not be able to handle a budget for more than a week. She speaks from experience: ["]If the money's there, they'll be inclined to spend it, to say, `oh, there was another bill to pay'. You won't hear about the extra pints."

She and her husband also insist that their children ring them if they run short, rather than borrow from other people.

While some parents fret because they never see their college-going child any more, others may be worried because they see too much of them. Mairead's daughter, like many other students, found college life overwhelming. She found it hard to make friends, was baffled by the disorganisation of college life, and incapable of fending for herself in this new situation.

She started sleeping in late, skipping lectures, and Mairead didn't know what to do. "I found I was standing helplessly by. I didn't feel I could ring up the way I would have when she was younger, I felt she should be able to sort it out."

It's undoubtedly true that for all the students going to college who have a ball and enjoy it thoroughly, there are plenty who find it very lonely. Says Murray: "It's a real rite of passage, a real mark of moving into adulthood, and it's very frightening as well as exciting." Parents should look out for signs that all is not well, she says - for many students will pretend that everything is okay, rather than admit that they had no one to go to lunch with, that they're not coping. "If they're coming home at the weekend, look at how they are as they get ready to go back to college on Sunday."

You have to be sensitive in raising the topic, to avoid making them feel like failures. It might be a good idea, she suggests, to ring the college's counsellor to get advice for yourself on how to handle the situation, especially if you fear your child is slipping into depression.

If this is the first month of the first time your first child has made this big transition, you've probably leaped over the first hurdles (the nervous breakdown when their train got in late, the shock that your quiet teen has turned into a party animal). Hmm . . . in a decade or so, they might actually be self-sufficient.