If the education reform movement has a guiding principle, it is accountability: the belief that test scores can be trusted as an accurate gauge of progress and used to reward flourishing schools or punish failing ones.

But a series of prominent cheating scandals across the U.S. has exposed a potentially fatal flaw in policies stemming from that belief. Intense pressure to demonstrate rising student achievement can lead educators to fudge test results and alter grades, making the ostensible progress a mirage and undermining the idea that test scores can be relied upon as objective.

The pressure comes partially from within school systems, where education officials alternately shutter schools and fire principals or shower successful schools with bonuses. It also emanates from the federal government. The Race to the Top program, one of President Barack Obama's early domestic initiatives, had states compete for education grants by demonstrating their commitment to reform measures including data-based benchmarks for student performance.

Now, there is mounting evidence that this focus on accountability may have backfired.

In New York City, where Mayor Michael Bloomberg has made tying performance bonuses and decisions about which schools to close to test scores a centerpiece of his education policy, an investigation by Special Commissioner of Investigation Richard Condon revealed that allegations of teachers tampering with test scores has steadily risen in recent years. Speaking to The New York Times, Condon explicitly faulted education policies that placed outsize emphasis on rigid metrics for progress.

When you start giving money to the schools to do well, that's another incentive to appear to do well if you are not doing well, Condon said. If a lot of the evaluation is based on how the students do, that's an incentive for the teachers to try to help the students do well, even in ways that are unacceptable.

Atlanta Case Study

In Atlanta, an investigation into test scores rising at a suspiciously high rate found a systemic practice of falsifying test results to make students appear to be peforming better than they were. Educators at 44 of 56 schools were implicated, and former superintendent Beverly Hall -- who was named Superintendent of the Year in 2009 for now-discredited gains -- stood accused of fostering a culture of fear, intimidation and retaliation.

I think the overall conclusion was that testing and results and targets being reached became more important than actual learning for children, Georgia Gov. Nathan Deal said. And when reaching targets became the goal, it was a goal that was pursued with no excuses.

And in Washington, D.C., where former education chancellor Michelle Rhee became a fiery and divisive standard bearer for education reform, a USAToday analysis found that schools exhibiting dramatic improvements in test scores also had improbably high rates of tests in which incorrect answers were erased and replaced with correct ones. That could mean that teachers were changing answers to elevate student progress, an allegation that Rhee has peremptorily denied while refusing to speak to USAToday.

This is like an education Ponzi scam, Nathan Saunders, head of the Washington Teachers' Union, told USA Today. If your test scores improve, you make more money. If not, you get fired. That's incredibly dangerous.