A former principal pleaded not guilty yesterday to indecently assaulting four female teachers at a primary school in Tseung Kwan O. So Yau-hang, ex-headmaster of Yan Oi Tong Tin Ka Ping Primary School, was in Kwun Tong Court to face 13 counts of indecent assault between 2000 and 2005. Two of the assaults allegedly took place in a private car and on a school staircase and the rest allegedly were in his office, the court heard. So, 53, was released on HK$20,000 bail. His trial will start on October 29.