But she and other European researchers have demonstrated that people with dementia can significantly improve their ability to do the tasks they’ve opted to tackle, their chosen priorities. Those improvements persist over months, perhaps up to a year, even as participants’ cognition declines in other ways.

“They want to be enabled to manage their lives,” said Dr. Clare. “It gives hope that they can handle everyday challenges.”

This approach may represent the future for the growing number of older adults around the world with dementia. Trials of drugs to prevent or treat dementia have failed over and over. Even if some future treatment demonstrated effectiveness, millions of people and their stressed family caregivers need help now.

“We can’t wait another 20 years for some magic pill,” said Laura Gitlin, dean of the College of Nursing and Health Professions at Drexel University. She has developed something called the Tailored Activity Program (T.A.P.), somewhat similar to cognitive rehab, which also brings occupational therapists into people’s homes.

“We’re trying to lay the scientific basis for nonpharmacological approaches,” Dr. Gitlin said. “These studies signal that they can have powerful effects on peoples’ lives.”

In the United Kingdom, for instance, a government-supported trial involving 475 people with early-stage dementia found that after cognitive rehab, most participants attained their goals, while those in a control group did not, and they maintained improvement at three months and at nine months. (The study has not yet been published; Dr. Clare presented the results at a conference last year.)