Finally, there's the issue of frequency, severity, and timing. Some research, such as a 2007 study reporting that spanking induces behavioral problems, lumps kids who were ever spanked into a single category and compares them with kids who were never spanked. But these subjects may have been spanked once in their lives (like me) or once a day for 10 years straight. Some may have been hit hard on bare buttocks, while others were spanked lightly on top of clothes. And all of this matters in terms of the impact of the spankings.
The 2010 study in Pediatrics, for instance, reported that 3-year-olds who were spanked were more likely to exhibit aggression when they were 5, even controlling for the kids' prior behaviors and the mothers' other risk factors (like depression). But the study only found these ill effects if the kids were spanked more than twice a month. Another study, published in April 2012, found that kids who were spanked once a month or less with hands (no objects) were no more likely to subsequently develop delinquent behavior than were kids who were never spanked at all. Kids spanked more frequently or with objects, however, did develop problems. Finally, research suggests that preschool kids are the least likely to get scarred from spanking but that striking infants or older kids could cause problems.
So spanking, it seems, can be safe. But is it effective? In a 2005 meta-analysis, researchers analyzed 26 studies that compared the effects of spanking with those of other disciplinary tactics. They found that when spanking was used as a backup, only on 2-to-6-year-olds, and wasn't done in anger, it helped to increase kids' compliance in both the short and long term compared with 10 other disciplinary tactics, including scolding, reasoning, and removing privileges. There are also four studies (published in 1981, 1983, 1988, and 1990) that did use randomized, controlled clinical trial designs to assess the positive effects of spanking in preschool kids with conduct disorders, reporting in all four cases that spanking when kids did not adhere to time-outs improved their subsequent behavior.