When did Georgia public schools add the 12th grade?

Georgia public schools didn't "add" a 12th grade at a specific point in time. High schools in the United States have generally evolved over time. While there wasn't a single date when a 12th grade was suddenly instituted across the state, the standardization of a 12-year public education system (including 12th grade) occurred gradually throughout the late 19th and early 20th centuries. There wasn't a specific year for Georgia.