WASHINGTON — Toddlers rescued from orphanages and placed in good foster homes score dramatically higher on IQ tests years later than children who were left behind, concludes a one-of-a-kind project in Romania that has profound implications for child welfare around the globe.

The boost meant the difference between borderline retardation and average intelligence for some youngsters.

Most important, children removed from orphanages before age 2 had the biggest improvement — key new evidence of a sensitive period for brain development, according to the U.S. team that conducted the research.

"What we're really talking about is the importance of getting kids out of bad environments and put into good environments," said Dr. Charles Nelson III of Harvard Medical School, who led the study being published Friday in the journal Science.

The younger that happens, "the less likely the child is to have major problems," he added.

The research is credited with influencing child-care changes in Romania, and UNICEF has begun using the data to push numerous countries that still depend on state-run orphanages to start shifting to foster care-like systems.

"The research provides concrete scientific evidence on the long-term impacts of the deprivation of quality care for children," UNICEF child protection specialist Aaron Greenberg said. "The interesting part about this is the one-on-one caring of a young child impacts ... cognitive and intellectual development."

That orphanages are not optimal for child development comes as no surprise. Earlier studies have found that thousands of children adopted during the 1990s from squalid orphanages in Eastern Europe, China and elsewhere continued to face serious developmental problems even after moving to affluent new homes with doting parents.

But questions remain. Were those abandoned or orphaned children who spent more time in orphanages less healthy to begin with? How much damage does neglect and lack of stimulation in the early months of life do? How long does that damage last?

In the study, U.S. researchers randomly assigned 136 young children in Bucharest's six orphanages to either keep living there or live with foster parents who were specially trained and paid for by the study. Romania had no foster-care system in 2000 when the research began.

The team chose apparently healthy children. Researchers repeatedly tested brain development as those children grew, and tracked those who ultimately were adopted or reunited with family. For comparison, they also tested the cognitive ability of children who never were institutionalized.

By 4 1/2, youngsters in foster care were scoring almost 10 points higher on IQ tests than the children left in orphanages. Children who left the orphanages before 2 saw an almost 15-point increase.

Nelson compared the ages at which children were sent to foster care. For every extra month spent in the orphanage, up to almost age 3, it meant roughly a half-point lower score on those later IQ tests.

Children raised in their biological homes still fared best, with average test scores 10 points to 20 points higher than the foster-care kids.

What does that mean as these children grow up? Just this week an anxious acquaintance cornered Nelson to ask what to expect of a child who spent nine months in a Vietnamese orphanage.

"There's much more to functioning in life than your IQ," Nelson stresses.

Plus, he only now has begun testing these children again as they turn 7 and 8. They might catch up.

For now, Nelson tells adoptive parents, "The older the child is when they leave the institution, the more likely that child may have some developmental problems and the more difficult it may be to ameliorate those problems. ... The message to parents is simply to go into this with their eyes open, but not to give up."

For the U.S. and other countries that depend on foster care instead of orphanages, the study has implications, too, because it used high-quality foster care that is not the norm in many places, Nelson noted. Studies comparing the impact of foster care of varying quality are under way.

The Romanian government requested the study and began its own foster care program shortly thereafter. Early study results are credited with influencing Romania's recent prohibition on institutionalizing children under 2 unless they are severely disabled.