The College Board has decided not to invalidate more than 250 Advanced Placement exams from a Montgomery County high school after a student took a cellphone video in the testing center and posted it on Twitter.

Quince Orchard High School Principal Carole A. Working reported a possible test security violation to the College Board after learning that a Gaithersburg student taking an AP psychology exam May 6 made the video. Exam policies prohibit cellphones, smartphones and tablets.

The 274 students who took that exam had been waiting since last week to learn whether the College Board was going to nullify the scores because of the video, which officials can do if deemed necessary “to protect the integrity of the exam,” according to the College Board’s guidelines.

AP tests, administered nationally each spring, measure a student’s grasp of various academic subjects on a scale of 1 to 5. A 3 or better on the exams can qualify for college credit.

Working said she and her students felt “an enormous sense of relief” after hearing this week that the test scores will stand.

The video that appeared on Twitter did not show the test materials or test questions, but it did show students walking down an aisle to take the exam. The video also captured something in bubble wrap, which Working said might have been the test.

Spokesmen for the county school system and Educational Testing Service — the company that handles administration and security for the AP tests — said they could not discuss whether the student who posted the video will have his or her test nullified, citing confidentiality rules. The testing company plans to communicate directly with the student. Tom Ewing, a spokesman, said he could not elaborate.

“All that I can say further [is] that there is a rule (which is clearly stated prior to testing), that the use of a cellphone in a testing center is grounds for dismissal and cancellation of scores,” Ewing wrote in an e-mail.

Working said the episode was a wake-up call about test security.

“There was a sense within the school and the community that we should review our [exam day] procedures — although I’m not sure that was the issue — to make sure something like this doesn’t happen again,” Working said.