In the fall of 2010, Ms. Parks, a third-grade teacher at Venetian Hills Elementary School in southwest Atlanta, agreed to become Witness No. 1 for Mr. Hyde, in what would develop into the most widespread public school cheating scandal in memory.

Ms. Parks admitted to Mr. Hyde that she was one of seven teachers — nicknamed “the chosen” — who sat in a locked windowless room every afternoon during the week of state testing, raising students’ scores by erasing wrong answers and making them right. She then agreed to wear a hidden electronic wire to school, and for weeks she secretly recorded the conversations of her fellow teachers for Mr. Hyde.

In the two and a half years since, the state’s investigation reached from Ms. Parks’s third-grade classroom all the way to the district superintendent at the time, Beverly L. Hall, who was one of 35 Atlanta educators indicted Friday by a Fulton County grand jury.