"When I started paying, my grade-point average doubled," said Holmes, who is independently wealthy after selling his insurance agency last year.

Holmes believes his children, age 13, 8 and 5, also will appreciate education more if they help pay for it, even if he's not around to supervise. So his estate plan includes a "family incentive trust" that would reward good grades, offer extra payments for graduate school and provide some, but not all, of his children's college tuition expenses to ensure they contribute to the cost.

Dismissed as an expensive and potentially ruinous fad by some legal experts, family incentive trusts have nonetheless captured the imagination of newly wealthy parents concerned about leaving too much money outright to their children.

Interest in the trusts has increased in the last few years as stock market and real estate booms have created hundreds of thousands of new millionaires, said John Jeffrey Scroggin, the Holmes' attorney and a leading advocate of family incentive trusts.

"I think the issues have been there all along. We just didn't have so many wealthy people thinking about them," Scroggin said.

Trusts that come with strings are not new--in fact, trusts by their very definition are designed to restrict the flow of inherited money to beneficiaries. For decades, concerned parents and other trust creators have designed vehicles that would apportion wealth over time, typically requiring the inheritor to reach some age milestone--21, 30, 35 or even later--before receiving distributions.

More rarely, trusts have included other requirements, such as that the inheritor be married or practice the same religion as the trust creator, before money was released.

Family incentive trusts, however, are adding much more elaborate riffs on this theme.

Affluent parents who want to encourage their children to work for a living may create trusts that match earned income dollar-for-dollar or link payouts to the beneficiaries' own efforts to increase their net worth. Parents who want to produce entrepreneurs can turn the trusts into seed-money generators, matching any cash the beneficiary raises from other sources.

Good grades, thrifty habits, sober living and even the birth of grandchildren can be encouraged with monetary awards, whereas those who fail to toe the family line could find themselves without funds.

Financial advisor Joe Saul-Sehy said one of his clients decided to promote sensible money management among her adult children by requiring them to pay off any credit card debt before they can receive trust fund distributions.

Saul-Sehy, who works for American Express Financial Advisors in Auburn Hills, Mich., acknowledges that the stipulation could be an easy one to get around. The trustee supervising the distribution would have to run credit reports on the children to determine their financial status. Even then the heirs could disguise their credit card debts by taking out a home equity loan to pay off the balances.

"Trying to rule from beyond the grave is futile. There is always a way to get around these incentives," Saul-Sehy said. Still, he said, the value of the trust is that it communicates to the children what the client wanted and valued, whether they ultimately choose to abide by the wishes or not.

The difficulty of enforcing many provisions of family incentive trusts is just one reason some legal experts--and advocates for beneficiaries--cast a skeptical eye on the documents.

Bob Whitman, an estate planning attorney and full-time law professor at the University of Connecticut, believes many people do not understand the expense and difficulties of administering a trust. He criticizes his peers for promoting "designer" versions that clients may not need.

"It's like Seventh Avenue designer gowns--down the runway comes the next fashion, and look at that, it's strapless," scoffed Whitman, who also serves on a national board of professors that advocates trust and estate law reform. "It's being put out there and people are blindly going for it."

Like other critics, Whitman says the trusts are no substitute for good parenting. After-death provisions that restrict payouts to adult children are redundant if the parents adequately conveyed their values during life, and superfluous if they didn't, he says.

"Think about the message you send to your children when you put money in trust," Whitman said. "You're taking away the responsibility of learning to use money, including making some mistakes."