Others described kids "screaming" as Rathburn blew up and "cursed" about the frustrating situation she was in as a mother.
The whole outburst was caught on the school's CCTV. Authorities said the vision showed her approaching the class and she could be seen to "lift her finger in a pointing manner and circle around as if making sure all the kids heard her and were listening".
Police were only alerted to the school-gate showdown when Rathburn later posted a six-minute, 44-second video on Facebook in which she said she'd "snuck into the school and confronted kids" who she said were about 9.
Three days after the incident, she was charged with interfering, disrupting or disturbing schools and released on a $1500 (US$1000) bond.
She's since said she regretted "allowing emotions to control" her behaviour in an interview with the local paper.
"I am absolutely ashamed of myself for the actions of walking up into that school," Rathburn told the Greenville News.
"You know, I owe the parents, the children and the staff an apology for that. Absolutely, it was wrong."
However, she described her growing frustration at her child being bullied, sharing emails to the school where she asked them to address her claims her son was called names, jerked back and hit with a computer.
After one incident where a student was allegedly making faces at her son, a teacher said he told Rathburn's son to "ignore him, stay away and be the bigger man, and I think it will stop", according to an email Rathburn shared.
But she claims when the school suggested separating her son from the rest of the class, she reached boiling point.
"Honestly, I don't know how I could have gotten my message across any other way," she told the outlet.
She's now been banned from the school property, a situation she described as "devastating".
"I can't go eat lunch with my children," she said.
"I can't watch them on field day ... that's devastating."
In response to the incident, Greenbrier, which calls itself the "school of kindness", has added a second staff member to work on the front door in the morning but they haven't commented on Rathburn's case.