TAIPEI, Taiwan—It was a call no parent wants to receive. On Mother’s Day, around 9 p.m., a woman in Chengdu in southwestern China was told that her son, who she had dropped off at school just hours ago, had died. Distraught, she went to Chengdu No. 49 Middle School immediately, but was not allowed to even enter the school grounds, she wrote in a series of Twitter-like Weibo posts on the next day that were shared hundreds of thousands of times this week. Her account, disputing both the police and local government’s account of her 16-year-old son’s death, has touched a nerve, becoming one of the most discussed topics on Chinese social media this week. One related hashtag #ChengduNo.49Middle# racked up more than 1.5 billion views alone on Weibo. People online called for justice for the mother and questioned the actions of the school, police, and local authorities. By May …