An investigation of the meltdown in the Tennessee computerized testing this past spring determined that there was no cyberattack, as the state education department originally claimed. Instead, the vendor made errors.

Questar’s unauthorized change of an online testing tool — not a possible cyber attack, as earlier reported by the company — was responsible for shutting down Tennessee’s computerized exams on their second day this spring, the state’s chief investigator reported Wednesday.

An independent probe determined that “there was no cyber attack,” nor was any student data compromised, when thousands of students could not log onto the online exam known as TNReady on April 17.

Instead, investigators said, Questar was mostly responsible for this year’s testing miscues. The main culprit was a combination of “bugs in the software” and the slowness of a computerized tool designed to let students turn text into speech if they need audible instructions.

Comptroller Justin P. Wilson reviewed early findings of his office’s internal review and the external investigation by a company hired by the Education Department during a legislative hearing in Nashville.

Education Commissioner Candice McQueen also told lawmakers that Tennessee is docking Questar about $2.5 million this year out of its $30 million contract because of the online problems that plagued many students and schools during the three-week testing window.

Payments being withheld are punitive, as well as to cover the state’s costs to address the problems, she said, adding that other discounts could follow.

Last week, McQueen announced that the state plans to launch a new search this fall for one or more testing companies to take over TNReady beginning in the 2019-20 school year. She said a track record of successful online testing is a must.

Will states ever figure out that online testing is less reliable than paper-and-pencil testing, and that teacher-made tests are more valuable than any standardized tests?