“Thus, among the 79 statistically significant effect sizes, 99 percent indicated an association between spanking and a detrimental child outcome,” the study reads. Those outcomes were: “low moral internalization, aggression, antisocial behavior, externalizing behavior problems, internalizing behavior problems, mental-health problems, negative parent–child relationships, impaired cognitive ability, low self-esteem, and risk of physical abuse from parents.”

Harsher forms of abuse were excluded from the analysis, so this paper shows that spanking alone puts children at risk for some serious problems. The authors also looked at a subset of studies that compared spanking with physical abuse, and found that both were linked to bad outcomes “that are similar in magnitude and identical in direction,” they wrote.
https://www.theatlantic.com/health/archive/2016/04/the-strong-evidence-against-spanking/479937/?utm_source=atlfb