A report out Sunday is the second major study within two weeks to condemn the practice of spanking children. But other experts raise questions and continue to debate the controversial discipline technique used in many American homes.

The latest study, presented at a Denver conference, gives an optimistic assessment of the effects of not spanking youngsters.

Children who are not spanked tend to be better behaved and do better in school, grow up to have better marriages, earn more money and live better lives, according to Murray Straus of the Family Research Laboratory at the University of New Hampshire. Straus summed up 50 years of research on the effectiveness and side effects of spanking. That mass of research indicates agreement among professionals on two things, he said in a statement released prior to the conference:

Spanking is not the most effective method of discipline. "Although spanking works, it does not work better than other methods of correcting and teaching kids." Spanking has harmful side effects. It increases "the chance that a child will become rebellious or depressed." These side effects may take years to show up, he says. "Lots of people are worried that if parents never spanked, the result would be kids running wild, higher rates of delinquency, and when they grow up, more crime," he says. "Actually, what the research shows is just the opposite."

Toddlers and young children who are not spanked tend to have faster mental development, do better in school and have a better chance of graduating from college, he says. They also hit other children less and grow up to be parents who tend not to spank.

The earlier comprehensive report also was critical of spanking, but found that it changes behavior. The child complies with the parent's wishes, said a study in the July issue of the Psychological Bulletin from the American Psychological Association. But the researcher also found 10 negatives linked with spanking that outweigh the fact the child stops misbehaving, including increased aggression and antisocial behavior. The practice also does not teach a child right from wrong.

Not all children who are spanked turn out to be aggressive or delinquent, wrote Elizabeth Thompson Gershoff, a researcher and psychologist at Columbia University. Many factors can moderate the punishment such as how well the parent and child get along. Studying the effects of spanking is difficult because parents differ in how often they spank, how vigorously they do it, how emotionally aroused they are when they spank — and how accurately they report such factors.

Gershoff evaluated 88 studies done over 62 years on corporal punishment by parents.

Experts differ on even the definition of spanking, but they worry that any suggestion it might be acceptable in the mildest of forms might lead to child abuse.