As if divorces aren't bad enough, one surprising bit of fallout of these falling-outs is the refusal of an ex-spouse to pay college education bills of a child. It has become such an issue that some states have passed laws that can force parents to pay, and many state courts have issued rulings that do the same thing.

Lili A. Vasileff of Greenwich, Conn., co-president of the Association of Divorce Financial Planners, says spouses sometimes hold back on paying for college just to get even. She said one of her clients had to raise all the money for her daughter's college education after her former husband refused to contribute.

"It was a vindictive move by the father," Ms. Vasileff said. "It penalizes the child for the divorce because he's getting back at the mother."

The issue seems clear-cut. What kind of parent would deny a child a higher education? Why not make that parent pay if he or she can afford it?

But the issue is not as straightforward as it seems, no matter what our emotions say. Indeed, not all states have taken action, and courts in one, Pennsylvania, have ruled that forcing divorced parents to pay is unconstitutional.

The considerations are many. What if the child had bad grades and poor attendance in high school? A reluctant parent may not think college is appropriate. Or what if a parent really can't afford the bill or is willing to pay for a child to attend a state university, but not a pricey private school?

A recently divorced woman, who asked that her name not be used, said that her husband had agreed to pay tuition only for a state school for their two children — and that she got that only after a fight.

"I was willing to say in the settlement that we would each contribute half," she said. "He said he wouldn't put it in writing, but promised he would take care of their college. I said: `I can't trust you. I thought you were going to stay here for better or worse.' He got hurt by that."

One divorce expert told me that one question "is the debate of the century": Why can divorced parents be forced to pay for their children's college tuition when married couples are not?

"Do we have a responsibility to give our children a college education? No," said Anita M. Ventrelli, a partner at the law firm of Schiller, DuCanto & Fleck in Chicago. "These laws really give children of divorce rights that children of nondivorced children do not have."

That is an interesting argument, but one that many courts have dismissed, said Laura W. Morgan, a lawyer in Charlottesville, Va., who is chairwoman of the Child Support Committee of the Family Law Section of the American Bar Association. "The courts say that married parents and unmarried parents can be treated differently under the law," she said. "What the law is trying to do is duplicate the support that the child would have received had the marriage remained intact. While it is true that married parents don't have the legal obligation to send their kids to college, the fact of the matter is that those who can afford to do so, do."

And it's a good thing. Tuition and fees rose 5.8 percent, on average, at four-year private colleges for 2002-2003, to $18,273, and 9.6 percent at four-year public institutions, to $4,081, according to a report released last fall by the College Board. Right now many schools are mailing out their fall tuition bills.

Ms. Morgan said that 16 states and the District of Columbia had rejected the traditional rule that child support ends at the age of 18. It is in those states that divorced parents can ask the court to step in to force the other spouse to pay, so long as they are willing to incur the legal fees involved. New York, New Jersey and Connecticut are among them.

Ms. Vasileff, the financial planner, said that before Connecticut passed its law last year, a divorced parent with no agreement about college would have to appeal to the other parent.

"You have moms with lower earnings capacity, and they were facing sending their child to college with limited resources," she said. "They would go back to the father and be in a begging situation."

Christopher Rone, associate director for financial aid at DePaul University in Chicago, said a divorced parent often pays the bill all alone. "Nine times out of 10 it is a mom who says, `I'm not getting any help from my husband.' "

Mr. Rone noted a common mistake when a divorced spouse files for aid: including the income of the other spouse in the application. Most schools want to see only the numbers for the custodial parent in making aid calculations. That helps the single parent. But he cautioned that some schools assume that the other parent will be paying part of the bill and assess what is called a noncustodial parent contribution. If that assumption is wrong, he advised, tell the school. "If you're not getting help," he said, "call to find out whether an N.C.P. has been added and what documentation could you submit to get that waived."

THE best solution, of course, is to reach an agreement on college while negotiating the divorce settlement. In other words, don't let your spouse leave home without it. The problem is, if the children are young, parents may not think of such agreements or may assume that the other spouse will pay when the time comes. That can be a big mistake, Ms. Morgan said, if you don't live in one of the states that allow you to revisit the issue.

"If you have a 2-year-old, paying for college 16 years hence is too much to think about, especially when you are going through the emotions of a divorce," she said. "But if you don't think about it now, you will be out of luck because you can't come back. The law does not protect people from bad bargains."

If you don't want to deal with the issue in the divorce negotiations, she said, you should add a provision to the settlement that will reopen it down the road.

"The agreement can be somewhat open-ended, and when the time comes you will apportion the costs according to your means," she said. "It can be an agreement to agree to particulars. But don't make it too ambiguous; otherwise it would not constitute a contract and will be nonenforceable."

Ms. Vasileff urges her clients in the states that do provide relief to agree before the courts become involved.

"If you don't come to agreement you can end up in court, and that's the worst position to be in," she said. "Then the judge decides, not the individual or the attorney. Most people settle, literally, on the steps of court."

It's hard for this issue not to cause a sad shake of the head. There is a feeling — and maybe it just comes from the heart — that the other parent will do the right thing. But Ms. Ventrelli, who has worked on enough of these cases, says parents often bring the problem on themselves.

"There are cases when they alienate the child against the other parent, not thinking that in eight years they will be going back to him saying, `Hey, pony up,' " she said. "But wasn't it just last week the kid said he didn't want to see his father again? Why does the father's reaction surprise you?"