It's understood an altercation flared at lunch time with the PSNI being asked to respond.
They remains at the scene this afternoon.
Police say there were no serious injuries and the parents of all students involved have been contacted.
This mother arrived at the school to collect her children, she was concerned trouble could flare again as the school closes:
Holy Cross College is a co-educational school which caters for 1500 students.
Holy Cross College was established in 2003 as a result of the amalgamation of three Catholic post-primary schools in Strabane; the Convent Grammar School, St Colman's High School and Our Lady of Mercy Secondary School.