Here is how the plan works. Families contribute to a trust and get a certificate representing a share of tuition at current rates, a proportion that remains constant even as tuition rises. So, for instance, if you were to pay in $10,000, and the tuition at a given college were $40,000, the certificate you bought would be worth a quarter of one year’s tuition at that college. If, in 10 years, the tuition is $60,000, your certificate would be worth a fourth of that amount, or $15,000. Money must be in the plan for at least three years before it can be used. The plan covers tuition and mandatory fees, but not room and board and other expenses, like books.

If your child chooses a college that is not in the plan, you can change the beneficiary of the account, so another family member or relative can use it. Or you can request a refund. But you will earn only 2 percent maximum on your savings in the plan, and you could be subject to a loss of as much as 2 percent, depending on the performance of the trust’s investments. (While the value of the tuition certificates are guaranteed, plan documents caution that refunds aren’t assured, if the trust lacks funds to pay them. But Ms. Farmer says it’s “hard to imagine a scenario” in which that would happen. Refunds have averaged about 1 percent of plan assets for the last five years.)

Irene Sang, an optometrist in South Pasadena, Calif., and a graduate of Occidental College, a plan participant, told her two children the plan had a specific menu of colleges, but she also assured them she would find a way to send them to whatever college they wanted. (She also saved in a traditional 529 plan.) Her daughter, Rachel, 17, won early acceptance last fall to Dartmouth College, which is not in the plan, and has an annual tuition of $43,782 a year.

Her son, Philip, 19, is a sophomore biology major at Johns Hopkins University, a plan participant. Ms. Sang plans to change the beneficiary on her daughter’s plan to her son, because his certificates did not cover all of his tuition. Then she will request a refund of the account balance, to use toward her daughter’s tuition.

She said the plan had served her well, although the family will probably have to borrow to finance part of her daughter’s education. “I have absolutely no regrets,” she said.

Brenna DeLaine, a doctor and medical director for an insurance company in Columbia, S.C., enrolled in the plan in part because she wanted Spelman College, a participant, to be an option for her daughter, Jai Brenay McQuilla. Ms. DeLaine is a graduate of Spelman, the historically black women’s institution in Atlanta. Her daughter visited the campus with her mother as a child and calls her mother’s best friends from college her aunts.

“I made saving a priority,” said Ms. DeLaine, who was alarmed at Spelman’s tuition increases. “No matter how tight it got, I paid into it.”