ROSS (CBS SF) — With new COVID cases on the rise, officials at Marin’s The Branson School announced Tuesday  the private high school was returning to only remote learning after students attended several Halloween parties where social distancing standards were not maintained and masks were not worn.

Head Master Chris Mazzola sent out a letter to parents whose children attend the private co-educational, college-preparatory high school located in Ross.

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“It came to our attention today that since we began in-person learning, there have been parties and social events in both Marin and San Francisco attended by Branson students,” Mazzola began her letter. “Based on information received over the weekend, we confirmed this morning from multiple sources that on Halloween, there were two parties in San Francisco, as well as another in Marin, that some of our students chose to attend.”

“We have also heard that many students were unmasked and not social distancing. To say this is disappointing is an understatement. We have been very clear, since March, about our expectations regarding parties and gatherings.”

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She continued telling parents that her team had worked hard to make sure standards in place that it allowed it to be among the few schools in the San Francisco Bay Area to return to in-class instruction at the start of the academic year.

“We have worked very hard to put the measures in place to allow us to safely bring our students and employees back for in-person learning,” Mazzola wrote. “Our administration, faculty, and staff have spent countless hours over the past several months refining our plans and safety protocols to make campus as safe as possible. We have set up a twice monthly testing protocol to limit the risk of the virus spreading in our community, which to date has been successful.”

But, Mazzola said, the parties were a violation of the school’s strict code of conduct and strong action was required.

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“In light of the news that some members of our community have not been abiding by our Code of Conduct, we cannot with confidence tell our employees, students or families that our campus provides an environment that is safe,” she wrote. “Branson is moving to fully remote instruction, effective Tuesday, November 10, until further notice. We have changed our testing this week from Friday, November 13 to Thursday, November 12 so that all students can come to school to test.