PALO ALTO (CBS SF) — Officials at Palo Alto High School have invalidated final exams taken by more than 100 students last month, after the school said they uncovered cheating.

According to the Bay Area News Group, the cheating took place in an Algebra 2 class where 112 students were enrolled.

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The newspaper said an investigation found students exchanged text messages and photos of answers to the test. According to the principal, some students finished the exam, which usually takes two hours to complete, in 30 minutes.

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Students in the Algebra 2 class will have an opportunity to retake the test, but they will have to put their summer vacation on hold. The retakes are scheduled for next Tuesday and August 13th. According to the school’s website, the last day of school was on May 29th. The next school year will begin on August 18th.

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The school said the retake is not mandatory and that students who don’t take the test will earn the same grade they had prior to the final.