(CNN) -- Think a little spanking won't do much harm to kids? New research says the effects can be long-lasting.

Children are too young to understand when parenting behavior is wrong, a social psychologist says.

Experts say "popping" kids can do more harm than good. A new study of more than 2,500 toddlers from low-income families found that spanking may have detrimental effects on behavior and mental development.

"We're talking about infants and toddlers, and I think that just, cognitively, they just don't understand enough about right or wrong or punishment to benefit from being spanked," said Lisa Berlin, the study's lead author and research scientist at the Center for Child and Family Policy at Duke University.

Berlin and colleagues found that children who were spanked as 1-year-olds tended to behave more aggressively at age 2, and did not perform as well as other children on a test measuring thinking skills at age 3. The study is published in the journal Child Development.

Although these effects were somewhat small, the study is just the latest of many supporting psychologists' advice against spanking. Still, some experts say spanking has a time and place.

The new study focused on children from low-income families because prior research suggested that spanking is more common among them, Berlin said. This may be because of the added stresses of parenting in a low-income situation, or because of a "cultural contagion" of behaviors among people. For example, in some families this study examined, a grandmother would spank a child, or neighbors would encourage physical discipline, she said.

Her study found that about one-third of the 1-year-olds, and about half of the 2- and 3-year-olds, had been spanked in the previous week, according to mothers' self-reporting to the researchers. At all three ages, African-American children were spanked significantly more frequently than those from white and Mexican-American families, and verbally punished more than the other children at ages 2 and 3, the study said.

Previous research had also found that parents who spank are more likely to be younger, less educated, single, and/or depressed and stressed, Berlin's study said. Spanking is most commonly used among parents who were spanked themselves, who live in the South, and/or who identify themselves as conservative Christians. These parents also tend to believe in the effectiveness of spanking or believe the child is at fault in a given situation, the study said.

The new research refutes the idea that more aggressive children are more likely to be spanked, Berlin said. On the other hand, the study did find that children who were fussier at age 1 were more likely to be spanked and verbally punished, she said.

Verbal punishment did not appear to have the same detrimental effects as spanking in this study, Berlin said.

Some remain unconvinced that parents should never spank their children. Robert Larzelere, associate professor of human development and family science at Oklahoma State University, conducted a meta-analysis of 26 studies on the subject, and found that, overall, spanking seemed more effective than 10 of 13 alternative disciplinary methods for getting a child to behave or do as asked.

Much of the research on the subject does not clearly demonstrate a causal link, Larzelere said. For example, in comparing studies, children who are spanked and children who are taken to psychologists both are more likely to have aggressive behavior later, he said.

The best use of spanking, Larzelere said, is in children between the ages of 2 and 6 when milder discipline tactics, such as time out, fail.

"That's why psychologists trained parents to use spanking that way for 25 years [from the] late '60s to mid-'90s," he said. Now, the trend of advice is away from spanking, but there's not much hard evidence to support it, he said.

Berlin's study focused on particularly early ages, Larzelere noted; much of the spanking literature focuses on ages 2 and older. Twelve months is probably too early to spank children, but there's no established point between ages 1 and 2 at which it is appropriate, he said.

Others say parents should not resort to spanking at any age. Susan Newman, social psychologist and author of "Little Things Long Remembered: Making Your Children Feel Special Every Day," said parents should discourage bad behaviors by taking away privileges such as dessert, or setting an earlier bedtime. They should also reinforce good behaviors verbally, saying how nice it is when their children share, for example.

The study corroborates what clinical psychologist Laura Markham, who was not involved in the study, has observed about the negative effects of spanking. Many mothers describe their children as fussy, resistant and demanding at age 1, which is a critical junction in the parent-child relationship, she said in an e-mail.

"If the mother sees this fussiness as willful misbehavior and begins verbally punishing or spanking, rather than empathizing with the child, the child's behavior deteriorates into more tantrums and other frustrating behavior," said Markham, who also offers advice at AhaParenting.com.

Newman also noted that children are too young to understand when parenting behavior is wrong, even at the level of abuse. Physical violence gets passed down in families because the only parenting skills people know are the behaviors that they saw at home, she said.

Spanking, moreover, reinforces negative memories in the child's mind, Newman said. Parents should aim instead to build "prominent, happy memories" of childhood for their kids, she said.

Regardless of income level, all parents can benefit from training classes, Newman said.

For future research, Berlin is looking at programs that work with low-income or high-risk families and try to promote supportive parenting behaviors.

In the spanking study, some mothers said they were receiving parenting services in which they were counseled not to spank their children.

"This is definitively the direction in which services are going and in which, in general, American culture is going," Berlin said.

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