In a shocking incident, a rowdy group of teens wielding knife and rods barged into a community school classroom and attacked indiscriminately, injuring a girl at Gothatar, Kathmandu on Thursday. A 15-year-old Hema Katuwal, eighth-grader at Tejbinayak Higher Secondary School sustained serious injuries in her left arm during the incident, police said. Three boys known for their unruly behaviour entered the school premises at around 10 am before blindly attacking students, police added. Police have arrested the perpetrators. They have been identified as Sulabh Pandit, Nabin Dahal and Abhinash Dahal, from Gothatar. According to school Principal Madhusudan Timilsena, Nabin is a former student at the school. He was expelled from the school three months of his admission. He barged into the classroom looking for one Bijay Nepali, it is learnt.