The Georgia teens were initially charged with attempted murder after more than a dozen students at their suburban Atlanta school got sick last November. The charges were reduced after the cake was tested.
An attorney for one of the girls says there was nothing "toxic" in the cake -- just some Elmer's glue, Tabasco sauce and a "Play-Doh-like substance."
The girls have been found guilty of disrupting a public school and were given nine and 12 months on probation. The judge also ordered them to write essays on what they learned.
The girls were transferred to another school and were allowed to return to class last month.
Last November, the father of one of two 13-year-old girls said he and his daughter were sorry it happened.
"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 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."