Major fears surrounding welfare overhaul have not come to pass, a study suggests. Preschoolers whose mothers left welfare for work did just as well in math, reading and behavior as those whose moms remained on welfare.

But the study also found no improvements for the children in welfare-to-work families, meaning the greatest hopes may be elusive as well.

When mothers went to work, they spent an average of 2.8 fewer hours each day with their young children, but brought home significantly more money. Researchers suggest those two factors may have balanced each other out to produce little overall impact on the children.

"When mom takes a job, you don't see big effects either way," said Lindsay Chase-Lansdale, a psychologist at Northwestern University who directed the study. "Children and teenagers were neither harmed nor helped in ways that people predicted."

Mothers did manage to make up most of the time they lost with their older children, and the study found some positive affects on young adolescents when their mothers left welfare or went to work.

The 1996 welfare overhaul, which required millions of poor single mothers to work and set limits on how long anyone could get monthly checks, helped cut the rolls by more than half.

Little was known at first about how children were affected. The latest findings add weight to a growing body of research that concludes there were few harmful effects for young children.

For teenagers, the evidence is more mixed. The new study, appearing Friday in the journal Science, found anxiety among teenagers dropped when their mothers went to work. But other research has found teenagers fared slightly worse in school, possibly because they were forced to spend more time watching over younger siblings.

The new study followed poor families living in Boston, Chicago and San Antonio. Most were black or Hispanic. About 38 percent were on welfare when the study began. It focused on 564 preschoolers, ages 2 to 4, and 895 adolescents, ages 10 to 14.

Lengthy interviews were conducted with the children and their mothers, first in 1999 and then about 16 months later to measure the impact, if any, of changing family circumstances. Tests included measurements of behavior problems and of cognitive ability, including reading and quantitative skills.

Researchers examined children who were on welfare in 1999 and then compared those who remained on welfare with those whose mothers had left assistance, including moms who were working and those who were not.

They also looked at mothers who were unemployed at the start of the study, regardless of whether they were on welfare. They compared children whose mothers had begun working by the second interview with those whose moms were still unemployed.

For young children, no differences could be discerned among any of these groups. Even children whose mothers were off welfare but still unemployed -- with no obvious source of income -- appeared no worse off than their peers.

"This study is an important reality check on the critics of welfare reform who have claimed it is going to hurt children," said Bruce Fuller, an expert in child development at the University of California, Berkeley, who was not involved with this study.

But he argued that the standard for success should be higher than do no harm.

"In 1996, from Bill Clinton to Newt Gingrich, policy-makers claimed welfare reform would help children and would break this intergenerational cycle of poverty," Fuller said. "It's unclear to me how we can argue welfare reform is working if the next generation is not any better off than their parents' generation."

Researchers caution that most of this study was conducted during strong economic times, suggesting the results could be different in a weak economy. Also, they note, they have only followed these children for a short time.

Still, those who supported the welfare changes were buoyed, and these findings are sure to be cited in the congressional debate over what changes are need to the welfare law.

"Almost all of our information is that preschool kids are not harmed" when mothers go to work, said Ron Haskins, a welfare expert at the Brookings Institution and a former congressional aide who helped write the 1996 law.

Haskins was encouraged that mothers were able to find time with their older children, even after they began working. The study found that mothers lost 3.7 hours per day of time with their older children while they were at work, but managed to make up all but 45 minutes of that by cutting back on personal, social and educational activities that did not involve their children.

Mothers who went to work also succeeded in earning more money. At the start of the study, families with an unemployed mother, including those on and off welfare, had an average income of $11,000. When the mom went to work, total household income rose to about $21,000.

Going on or off welfare alone, however, did not appreciably change family income.