Physical harm does more than put a child at risk for things like broken bones and cuts, although these are certainly significant issues. Corporal punishment also reduces brain matter and causes declines in IQ, according to Harvard Medical School psychiatrist Akemi Tomodo in a study of 1,455 individuals published as, “Reduced Prefrontal Cortical Gray Matter Volume in Young Adults Exposed to Harsh Corporal Punishment“ in Neuroimage in 2010. It is likely that the fear and pain experienced by children causes the stress response to increase. This alters brain development when the energy is put into being on alert for danger instead of learning.

Children who are spanked regularly as a form of punishment have less verbal ability at age 5 then their counterparts who are not spanked. They also show more externalizing behaviors such as aggression, according to Columbia University professor Michael MacKenzie and his colleagues in a study of 4,200 children published as “Corporal Punishment and Child Behavioral and Cognitive Outcomes Through 5 Years-of-age” in Infant and Child Development in 2014. Those who are hit tend to have less ability to recognize sounds and more trouble speaking than those who are not physically punished, which may affect both academics and social functioning. Researchers encourage a step away from belts and smacks and toward other alternatives, which may include open discussion or "time ins" where parents sit with their children until they calm down and can be spoken to calmly.

Physical punishment leads to anxiety and aggression, says Duke University professor Jennifer Landsford and her colleagues in a study of 1,196 children published as “Corporal Punishment, Maternal Warmth, and Child Adjustment” in the Journal of Clinical and Adolescent Psychology in 2014. These behaviors can affect children at school and may get them into trouble or cause other children to avoid them, leading to social issues. Even when maternal warmth — like cuddling or other support behaviors — is high, these effects still occur in response to physical punishment. Embracing maternal warmth and support without the physical punishment may be more effective in increasing connection and providing children with a base for wanting to please the parent. This may reduce unwanted behaviors and lead to less anxiety and aggression overall.

Not only does hitting increase negative behaviors like aggression, but any amount of spanking is ineffective overall, notes University of Texas professor and researcher Elizabeth T. Gershoff in an article published as “We Know Enough Now to Stop Hitting Our Children” in Child Development Perspectives in 2014. While some children stop a behavior in the short term after a spanking, they are more likely to continue to do it in the long term, especially when parents are not around. Using discipline techniques that explain more concisely why these behaviors are wrong on a level other than, “Because you’ll get hurt if you do it,” is essential to stopping behaviors in the long term and reducing negative behaviors that increase with hitting.