Among the knocks against families with “only children,” one of the most troubling is that these kids will be lonely.

New research suggests parents needn't worry. Children who grow up without siblings have just as many friends as peers with them, according to findings published Monday.

In a study of more than 13,000 American students from Grade 7 to 12, subjects were asked to name up to five girls and five boys at their school they considered friends. Students were nominated an average of five times by their schoolmates – and having siblings had no impact.

“By the time they get to adolescence, the people who had siblings don't fare any better or any worse than the ones who don't,” says sociologist Donna Bobbitt-Zeher, who presented the research at the annual meeting of the American Sociological Association in Atlanta.

Previous research in 2004 by Dr. Bobbitt-Zeher's co-author, sociologist Douglas Downey, suggested otherwise. Using data from another study, Dr.Downey found that kindergartners who were only children were rated by teachers as having poorer social skills than those who had siblings.

But the new research shows that the pattern does not persist as a child ages. Dr. Bobbitt-Zeher speculates that starting in kindergarten, interacting with peers both in school and during extra-curricular activities allows only children to overcome any disadvantages.

The research used data gathered from the National Longitudinal Study of Adolescent Health, which interviewed middle- and high-school students at more than 100 schools during the 1994-95 academic year.

The findings challenge the common thinking that a sibling provides a child with a partner to practise social skills, say Dr. Bobbitt-Zeher, an assistant professor of sociology at Ohio State University. “It may be true when they're younger, but we're not finding it here.”

The researchers controlled for family characteristics that are known to affect family size and which also affect social skills, such as socio-economic status and parental age. “None of those things changed our findings,” she says. Nor did any difference in the number of siblings, the gender or whether they were half-siblings, step-siblings or adopted.

Dr. Downey has also followed up with the same kindergarten group he studied in 2004 and found that differences in social skills between kids with and without siblings seem to fade by Grade 5.

The findings add to a growing body of research on the role of siblings. Most social science research has looked at the cognitive outcomes of having siblings, finding that children from larger families tend to do worse on educational tests than children from smaller families.

That research has generally suggested that having larger families dilutes the resources – emotional and financial – that can be given to any one child, says Dr. Bobbitt-Zeher.

And with fertility rates on the decline in much of the industrialized world, there is a particular interest in the effects of having fewer siblings – or none at all.

“We did come into this study wondering, from a population perspective, what might the consequences be?” says Dr. Bobbitt-Zeher. “These findings suggest they may not be as dire as many people would have expected.”

She's interested in further research on whether sibling relationships do benefit a person later in life, such as when caring for an ill or aging parent.

While Dr. Bobbitt-Zeher says she wouldn't suggest parents make any decisions about whether to have a second child based on her study, she does see an immediate benefit for parents of only children.

“It provides a little bit of assurance.”