Siblings between ages 4 and 8 can have up to eight fights an hour, Northeastern University psychology professor Laurie Kramer says. If you don't live with children this age, that stat may seem a tad dramatic; if you do, you're probably nodding your head.

Relationships with our brothers and sisters are among the most enduring and significant many of us will have in our lives, says Kramer, a clinical psychologist whose research focuses on the dynamics between young siblings. They're also some of the most common: Approximately 80% of families in the United States have two or more children. When they aren't getting along, it presents a potent, ubiquitous stress on parents.

"Parents often feel they don't have a lot of tools at their disposal," says Kramer. "I've long been interested in how to help families help their kids get along, from a scientific perspective."

For over a decade, "Fun With Sisters and Brothers", a program Kramer developed with a small team of childhood psychologists, has tried to answer those questions with in-person and online training for parents and children. In a new paper for the academic journal "Family Relations," the team set out to quantify the effectiveness of the online program (called "More Fun With Sisters and Brothers"), which consists of a series of asynchronous modules to teach parents how to intervene effectively in sibling conflicts.

Through a series of surveys, mothers who completed the program reported that their children demonstrated "greater sibling warmth," and "less antagonism and rivalry," according to the paper's abstract, adding that those positive effects were still strong months after the training's conclusion. (Fathers participate in the program as well, but the study sample focused on responses from mothers.)