Why did 178 Atlanta educators get caught changing students' test answers?

Because the test scores themselves had become the goal, not just a way to check whether students were learning. In 2009, teachers and principals across dozens of schools in the Atlanta Public Schools district corrected answers their students had entered on state standardized tests, in what became one of the biggest cheating scandals in American history. Teachers who confessed blamed inordinate pressure to hit the district's targets.

The pattern was predicted decades earlier by the psychologist Donald T. Campbell, who wrote what's now called Campbell's law: the more any quantitative social indicator is used for decision-making, the more it becomes subject to corruption, and the more it distorts the very process it's supposed to measure. Campbell specifically warned about achievement tests in 1976, writing that they can be valuable indicators under ordinary teaching, but once test scores become the goal of teaching itself, they both lose their value as indicators and distort education.

Atlanta's scandal fits that warning. The district had been celebrated for its test-score gains: between 2002 and 2009, its eighth-graders' scores on a national reading test rose 14 points, the biggest jump of any urban area. Then The Atlanta Journal-Constitution published an analysis showing statistically unlikely swings on the state's own tests, and a state investigation followed. It found that 44 of the district's 56 schools had cheated, implicating 178 educators who had corrected students' answers themselves. Teachers who admitted to it described inordinate pressure to hit targets, with the threat of a bad evaluation or losing their job if they didn't.

The case dragged through the longest criminal trial in Georgia history, and on 1 April 2015, eleven of the twelve defendants were convicted of racketeering. Once the test score had become the target, the test had stopped measuring what it was meant to measure.