Buses left Hatboro-Horsham High school around 10:30 a.m.
The school district said rumors were shared with the administration of potential safety concerns, and they received several tips.
Parents told 6abc there were several fights at the school on Friday.
Police had already been called to the school on Thursday for two fights and an assault on an administrator.
On Thursday, a school district spokesperson confirmed two unrelated altercations between students and a third incident with a student assaulting a school administrator. Some students involved were taken into police custody.
Friday's safety concerns were not yet detailed by police or the school district.
"I'm not even sure why they opened today after what happened yesterday," said one parent of a middle schooler. "I am so worried because one of my kids will be going to that school next year, and unfortunately the middle school is almost just as bad. There's no accountability for the kids' actions. Some of these kids seem completely uncontrollable, and nothing is done so they continue to act that way."