"It was a horrible prank that went too far and a lot of people have suffered," the father told The Associated Press. The man asked that he not be identified by name to protect his daughter.
The girls were held on assault charges Wednesday, a day after handing out the cornbread cake at East Cobb Middle School.
Lab tests showed the icing contained an expired prescription drug, bleach, clay and hot-pepper sauce, police said. Eleven students who ate it were treated at a hospital and released.
Both teens were charged with 12 counts of aggravated assault with intent to commit murder. One girl was also charged with terroristic acts and interference with government property. Both are still in custody, the father said.
Because the investigation is ongoing, Cobb Police Department spokesman Dana Pierce declined to comment on exactly how dangerous the cake was believed to be, saying only that it was potent enough to cause nausea, vomiting and diarrhea.
The father said the two girls had been bored Tuesday and began playing around in the kitchen.
"It was not any kind of malicious intent," he said. "They thought it would be funny. They know it's not funny now."
The father said his daughter was diagnosed this summer with Asperger's syndrome, and that doctors told him the girl should not be in a conventional school setting. Asperger's is an autism-related condition characterized by social and communication deficiencies.