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When a teacher wanted to measure just how many disruptions cell phones cause in class, she asked students in one class to turn the volume up on their phones. Each time they received a notification, she asked them to put a tally next to the type of notification they received.

By the end of the class, the board was filled with hundreds of tallies.

Joe Becigneul, who is a trustee at the Greater St. Albert Catholic Schools in Alberta, Canada, posted the teacher’s picture and it went viral.

It was shared more than 28,600 times.

Becigneul wrote, “Every one of these tally marks is an interruption in a students education.”

He called cell phones “toxic” to a learning environment.