By the numbers, it’s a paltry handful. Of more than 100,000 public schools in the United States, about 300 recently have faced suspicions, allegations and, in some cases hard proof, that teachers and administrators cheated to inflate standardized test scores.

But the impact of revelations in Atlanta, Baltimore, Philadelphia, Washington and other cities extends beyond those modest numbers. Questions raised in these incidents have sent tremors through the movement to hold schools and teachers accountable for student achievement through annual testing.

Within the next few years, a new generation of standardized tests is expected to be launched across the country to measure whether students are meeting common academic standards in English and math. Test score data will be the life blood of new systems for rating teachers and schools. A lack of public confidence in the integrity of testing could deal a serious blow to this agenda.

What’s more, questions about possible cheating have focused on big cities at the center of the school reform debate, where rising scores had generated cautious optimism about efforts to raise the performance of children from poor families.

“It’s a real blot on the copy book that needs to be addressed one way or the other. You can’t just sweep this under the rug,” said Chester E. Finn Jr., an assistant education secretary in the Reagan administration and president of the Thomas B. Fordham Institute, an education think tank. He said cheating allegations should be vigorously investigated and wrongdoers punished.

In June, Education Secretary Arne Duncan urged state education chiefs to get tough on cheating.

“Even the hint of testing irregularities and misconduct in the test administration process could call into question school reform efforts and undermine the state accountability systems that you have painstakingly built over the past decade,” Duncan wrote in a letter.

Duncan also confirmed this month that he has been in discussions with his department’s inspector general about evidence of test irregularities in some cities, including Atlanta and Washington. A spokesman for the D.C. inspector general said that Education Department investigators were assisting a local inquiry.

Skeptics of test-driven accountability say that such investigations show how standardized testing has skewed public education, driving some teachers and principals to cross ethical and legal lines to protect their jobs. The incidents have added energy to an emerging backlash from teachers who contend that they have been unfairly pilloried for underachieving schools.

“High-stakes testing inevitably winds up in distortions like this,” said Kenneth Bernstein, a government teacher at Eleanor Roosevelt High School in Greenbelt and one of the organizers of a “Save Our Schools” rally planned in Washington on July 30.

Testing advocates reject the notion that increased pressure spawns cheating. Andres Alonso, chief executive of Baltimore schools, where officials uncovered cheating on state tests at two elementary schools in 2009 and 2010, told the Baltimore Sun that such episodes reveal only that “unethical people are going to do unethical things.”

Cheating has been around as long as testing. Usually the concern in schools is about students using crib notes or other covert tactics to raise scores. Over the past 25 years, however, adult misconduct has emerged as a periodic issue in school reform. A 1992 cover story in U.S. News and World Report described a testing system “rife with abuse,” attributing the problem, even then, to pressure on teachers and administrators to improve scores.

The 2002 No Child Left Behind law — which mandates staffing changes and other sanctions for schools that fail to meet annual progress benchmarks — raised the stakes for educators. Superintendents saw their political fortunes flourish or flounder on the strength of test scores. Recently, teachers have begun to collect bonuses for their contributions to high-performing schools.

The recent disclosures of testing irregularities vary in depth and detail from city to city. Most were triggered by analyses showing high rates of wrong answers erased and changed to right ones on answer sheets.

In Atlanta, a 10-month state investigation found that 178 teachers and principals at 44 public schools tampered with answer sheets or gave improper help to students in 2009.

The 800-page report made public this month painted a harrowing picture of fear, obstruction and cover-ups during the tenure of former superintendent Beverly Hall.

At one school where a teacher confessed to cheating, investigators found, the principal “walked by her classroom often and said, ‘I need the numbers, I need the numbers.’” Investigators also reported that a principal “forced a teacher with low [state test] scores to crawl under a table at a faculty meeting.”

Hall’s successor has placed four senior school officials on paid leave. Others implicated in the wrongdoing have been given a grace period to resign or be fired. Hall has denied any knowledge of the cheating.

Pennsylvania officials announced an investigation this month of 89 schools, including 35 in Philadelphia, for irregularities on 2009 tests, including improbable gains in scores and suspicious erasure rates. The New Jersey Department of Education has launched a similar probe of 34 schools, including six in Newark.

Concerns about test security in the District surfaced in 2008, after more than 20 charter and regular public schools showed gains of 20 percentage points or better in reading or math proficiency on that year’s city tests. An erasure analysis by test publisher CTB McGraw-Hill eventually flagged more than 300 classrooms across 96 schools for suspicious erasure rates.

D.C. education officials discussed in 2008 and 2009 whether to investigate the schools with the highest erasure rates but decided not to press the matter.

This year USA Today reported elevated erasure levels were on a broader scale than previously acknowledged, involving more than 100 D.C. public schools from 2008 to 2010. Some classrooms showed rates so high that the odds that they were generated by random chance were many millions to one. The District’s inspector general is looking into the newspaper’s findings.

An investigation by Caveon, a Utah test security firm retained by the school system, led to the invalidation of 2010 test scores in three classrooms and the dismissal of two teachers.

Some D.C. school activists say questions will not be fully answered without a broader probe. In Atlanta, two former state prosecutors were given wide-ranging powers and extensive staff to obtain testimony from school employees.

“By any measure, what’s warranted in D.C. is at least the kind of investigation that was done in Atlanta,” said Mark Simon, a parent at School Without Walls High School in Northwest Washington.

D.C. Schools Chancellor Kaya Henderson, who last fall succeeded former chancellor Michelle A. Rhee, said she welcomes local and federal scrutiny of test scores. But she also said she is convinced that there is no Atlanta-sized scandal incubating in the District.

“What surprises me about Atlanta is that people were able to keep such a widespread practice quiet,” Henderson said. “I believe we have educators here who would blow the whistle, and I have not gotten that. Every instance when people have flagged somebody, our team is out there. It’s not in my interest to hide cheating.”