Working mothers can stop feeling guilty about the damage they've inflicted on their children by dropping them off at day care.

A recent study that looked at academic achievement and behavioral issues of children whose mothers work versus those with moms who stay home found that the kids of working moms don't turn out to be much different than those with stay at home moms in terms of academic achievement and behavior issues.

An analysis of 50 years of research examined 69 studies conducted between 1960 and March 2010. It determined that overall, children whose mothers return to work early in their lives, before age three, are no more likely to have significant behavior or academic problems than kids whose moms stay at home.

However, the researchers did find some small effects, both positive and negative, when they broke the results down into various sub-groups of children.

For example, children from middle- and upper-class, two-parent families performed slightly worse on formal tests of achievement and showed a slight increase in behavior problems when their mothers worked full-time during the first three years of their lives.

On the other hand, children from low-income, single-parent families actually did better on achievement tests and had fewer behavior problems when their moms were employed.

Therefore, the answer to the question of how a child will be affected by a working mother is, "it depends."

Rachel Lucas-Thompson, assistant professor of psychology at Macalester College, and author of the study said that hopefully, these findings will reassure mothers "that they're not screwing up their kids by going back to work."

A possible explanation for the positive effects seen in some children is that, for low-income or welfare-dependent households, the extra income from a working mother may reduce family stress. And for single-parent households, an employed mother might be a better role-model for her children. These benefits could outweigh any potential negative consequences of maternal absence.

However, in households where there isn't a pressing economic need for the mother to work, the extra income might not outweigh the advantages of always having a parent around. It might be a mistake to discount the negative results seen for some children just because they are small effects.

Jay Belsky, professor of psychology at Birkbeck University of London said the effects we're talking about are not likely to be visible to the naked eye. While these results -- good, bad or indifferent -- do not really offer much guidance to any individual parent struggling with the issue, they might offer guidance to policy makers.

Belsky says he would support a parental leave policy that would let parents stay home for the first year of a child's life.

The analysis found that the timing of a mother's return to work was very important. Going back to work before your child is one year old was associated with small decreases in later academic success, while employment during the second or third year of life was linked with increases in achievement. Working full-time during the first year was connected to more behavior problems, but working only part-time wasn't.

One factor that wasn't examined by the analysis is the type and quality of a child's alternative care. Kids who spend all day with a relative might have different outcomes than children who go to a day-care center. And little is known about how a father's employment affects children.