MILLBRAE — In a rare move that has Mills High School in an uproar, the College Board and Educational Testing Service have invalidated the Advanced Placement test results of as many as 224 students, citing “seating irregularities” when the 11 exams were taken in May.

Students are now demanding that the College Board reinstate the test scores, which have not been disclosed, rather than readminister the tests next month. They claim their scores may suffer in retaking the exams, and some graduating seniors say the delay is disrupting their college enrollment.

Incoming senior Gavin Wong learned of the problem Wednesday, when his family received a letter from Mills about the cancellation. The school said that, despite the seating problem, the scores “were not invalidated as a result of student misconduct,” according to a copy of the letter provided by Wong.

“Students aren’t to blame,” said Wong, 17, “but we are being punished harshly.”

ETS spokesman Tom Ewing said the school’s failure to follow administration guidelines on roughly 600 tests may have enabled some students to gain an unfair advantage, though ETS has not investigated whether there was any cheating.

“In situations like that it’s impossible to tell one way or the other,” Ewing said. “That’s why we had to cancel it.”

As the developer of AP and other standardized tests, ETS issues detailed guidelines to schools across the country and abroad for administering the exams. Those protocols cover seating, Ewing said, including the allowable distance between individual desks. In cases where more than one student is at a table, the guidelines enumerate how big the table has to be and where the students are permitted to sit.

It was unclear Friday if most or all of the AP tests at Mills were invalidated. Kirk Black, associate superintendent of the San Mateo Union High School District, said 224 students at Mills took the tests, ranging from biology and chemistry to English and history.

District officials met with several dozen Mills parents and students Thursday morning. Mills High School has scheduled two meetings on the tests next week at 7 p.m. Monday and Wednesday in the West Gym.

Black said late Thursday the district was still trying to get answers from the College Board and ETS as to what went wrong.

“We’ve never heard of this,” Black said of the mass cancellation of scores. “The whole thing seems out of the ordinary to us.”

Students at Mills have created a website (http://whyweneedourscoresback.com) on which numerous students have outlined their concerns. Several commenters identifying themselves as students said not having their scores is affecting their ability to register for college classes.

Gavin Wong’s brother, Mitchell, an 18-year-old incoming freshman at UC Berkeley, said he took four AP tests, and not having his scores has kept him from opting out of introductory English. Not being able to skip ahead to more advanced classes, the Wongs said, could ultimately cause financial problems for families of Mills students who had planned to graduate college early but are forced to add an extra semester.

The Wongs said they did not notice anything unusual about the seating during their tests and that students were well-spaced.

Based in Princeton, N.J., ETS distributes and scores more than 50 million tests a year. It develops, administers and scores AP tests for the College Board.

The organization will readminister the tests to Mills students in the next two to three weeks. The Wongs said they were much better prepared to take the test in May after an entire school year’s worth of preparation. Students are rusty now, they said. Some have travel plans; others were hoping to arrive at college early.

But ETS does not plan on reinstating the scores, said Ewing. The school’s failure to follow guidelines is a “dealbreaker.”

“We can’t report these scores,” he said. “We have to report scores that are valid to universities and colleges.”

It is “fairly uncommon” for an entire school, or test center, to have its scores canceled, said Ewing, adding the organization looked into the testing environment at Mills after receiving a tip. More than 300 students in the Orange County community of Mission Viejo reportedly had their scores invalidated in 2008.

Contact Aaron Kinney at 650-348-4357. Follow him at Twitter.com/kinneytimes.