The more time children spend watching television the poorer they perform academically, according to three recently published studies.

Excessive television viewing has been blamed for increasing rates of childhood obesity and for aggressive behavior, while its impact on schooling have been inconclusive, researchers said.

But studies published on the topic in this month's Archives of Pediatrics & Adolescent Medicine concluded television viewing tended to have an adverse effect on academic pursuits.

For instance, children in third grade (approximately 8 years old) who had televisions in their bedrooms -- and therefore watched more TV -- scored lower on standardized tests than those who did not have sets in their rooms.

In contrast, the study found having a home computer with access to the Internet resulted in comparatively higher test scores.

"Consistently, those with a bedroom television but no home computer access had, on average, the lowest scores and those with home computer access but no bedroom television had the highest scores," wrote study author Dina Borzekowski of Johns Hopkins University in Baltimore.

American homes with children have an average of nearly three televisions each, the report said, and children with televisions in their bedrooms averaged nearly 13 hours of viewing a week compared to nearly 11 hours by children who did not have their own sets.

The American Academy of Pediatrics has urged parents to limit children's television viewing to no more than one to two hours per day -- and to try to keep younger children away from TV altogether.

LIMITED BENEFITS

In two other studies published in the same journal, children who regularly watched television before the age of 3 ended up with lower test scores later on, and children and adolescents who watched more television were less likely to go on to finish high school or earn a college degree.

University of Washington researchers reported that 59 percent of U.S. children younger than age 2 watch an average of 1.3 hours of television per day, though there is no programing of proven educational value for children that young.

Their analysis of 1,800 children over a decade showed television watching was linked to poorer cognitive development among children younger than 3 and between the ages of 6 and 7.

TV watching appeared to help 3- to 5-year-olds with basic reading recognition and short-term memory, but not reading comprehension or mathematics, so the net effect of television watching is "limited in its beneficial impact," wrote study author Frederick Zimmerman.

Similarly, Robert Hancox of the University of Otago, Dunedin, New Zealand, found that children and adolescents who watched more television had less educational attainment regardless of their intelligence, socioeconomic status or childhood behavioral problems.

But condemning television as a vast wasteland -- government regulator Newton Minow's oft-quoted diatribe against the medium -- would be unfair as programing is not "monolithic," an editorial accompanying the studies said.

"Parents should be encouraged to incorporate well-produced, age-appropriate educational TV into their children's lives. Such programing represents a valuable tool for stimulating children's cognitive development," wrote Ariel Chernin and Deborah Linebarger of the University of Pennsylvania.