Florence police say Denise Dupree, 24, beat her six-year-old son with a cable cord in December.
Officers arrested her on charges of Unlawful Conduct Toward a Child Friday afternoon.
Lieutenant Tim Compton says a staff member at the child's school reported seeing bruises on the boy and alerted the school's resource officer.
After a lengthy investigation, officers got warrants to arrest Dupree.
The child was removed from Dupree's home at the start of the police investigation and placed in protective custody with a relative, according to Compton.
Dupree is being held at the Florence County Detention Center.
