Working mother associates poorer cognitive and verbal development of her child.

The study done by Teacher College gives us more information how does mother's full time working affect her child:

"Full-time employment by mothers by the ninth month of their child's life is associated with poorer cognitive and verbal development for these children at age three, according to a study conducted by Professor Jeanne Brooks-Gunn of Columbia Teachers College and Jane Waldfogel and Wen-Jui Han, both professors at Columbia's School of Social Work. The findings are published in the July-August issue of "Child Development."

The researchers also found that the quality of child care, the home environment and maternal sensitivity are important contributors to verbal and cognitive development during the first three years of life. However, even after taking these factors into account, the researchers found lower cognitive development for the children of mothers who worked full time (30 or more hours per week) during the first nine months of life.

The researchers did not find significant negative effects on cognitive and verbal development among children whose mothers worked fewer than 30 hours per week in the first year or those whose mothers who began work one year after their birth.

"We're not saying working is negative -- we're saying working a lot of hours in the first year of a child's life is associated with poorer cognitive and verbal development," said Brooks-Gunn. "If it's in young children's interest to have mothers working fewer hours, then that must be reflected in our policies."

"Western European countries have much more generous family-leave policies, reflecting people's concerns about the well-being of children," she noted. "We can do better in this country by taking results such as ours and not using them to say women shouldn't be working and instead ask what can work best for families in America so that mothers can work fewer hours when their children are younger."

The study published in "Child Development" used data on 900 white children from the National Institute of Child Health and Human Development Study of Early Child Care. The study included detailed data on maternal employment as well as data about the home environment, parental sensitivity and child-care quality and type over the first three years of life. Cognitive development was measured through the Bayley Mental Development Index (MDI) at 15 months, the revised Bayley MDI at 24 months and the Bracken School Readiness score at 36 months.

In other work, the authors have found that the negative effects of full-time maternal employment in the first year of life on children's cognitive development persist to age seven and eight. Following children from the National Longitudinal Survey of Youth's Child Supplement, they found that children whose mothers worked more than 20 hours per week in the first year of life scored lower on math and reading tests at age five and six and again at age seven and eight. This study was published in "Demography" in May 2002.