Cheating inquiries are under way in all Texas's major cities following a Dallas newspaper probe uncovering huge test-score swings from one year to the next and marked variations across a range of subjects at nearly 400 schools.
Last week, Texas education chiefs announced a crackdown on cheating with the appointment of a new test-security tsar.
"This whole situation is so embarrassing," said Texas education commissioner Shirley Neeley, announcing the measures.
Staff caught cheating face being banned from classrooms or up to 10 years'
imprisonment, Ms Neeley warned. "Texas educators understand that cheating on the test can be a career-ending move."
Several schools under investigation had been held up as models. Houston's Wesley elementary was feted by President Bush when he was Texas governor, and by television chat-show host Oprah Winfrey, as a school bucking the odds with at-risk students.
Now officials are investigating allegations that staff were expected to administer tests "the Wesley way", prompting students and filling out answer sheets themselves.
Impressive test-score improvements by Texas schools have been credited to accountability policies pioneered by Mr Bush as governor that have formed the blueprint for the White House's No Child Left Behind Act. Under the reforms, schools that fail to hit test targets face sanctions culminating in mass firings and closure.
The cheating allegations follow revelations in 2003 that Houston officials manipulated drop-out data and other statistics to inflate schools' standing in performance league tables. More than 24 Houston schools are currently being probed for cheating.
Across America a rising incidence of cheating highlights the pressures teachers face with school reputations, bonuses and jobs often riding on results, said test expert Thomas Haladyna, an education professor at Arizona state university. "There's pressure to get high test scores at any price," said Mr Haladyna.
Incidents he has seen include staff drilling students using questions taken directly from tests they are due to sit.
In September, test results for nine Mississippi schools were discarded following at least 25 suspected cases of cheating.
In July, results from nine education authorities in Arizona were voided because staff gave students extra time or read portions of tests aloud.