A study reveals smacking your child could be causing long-term damage. The lead researcher says 'smacking is never necessary'. Elizabeth Gershoff was part of a team made up of researchers from the University of Texas and the University of Michigan who looked into the risks associated with physically disciplining a child. They used five decades of research involving more than 160,000 children to form what they call a 'meta-analysis' — an average of all the research to date. Their conclusions, published in the Journal of Family Psychology, show that smacking is associated with several unintended outcomes. They include mental health problems, lower cognitive ability and a risk of accepting physical abuse as a norm later in life.