St. Theresa's Convent Sr. Sec. School (informally termed, STCS) is a Catholic private school, teaching students in Kindergarten through twelfth grade from Karnal in Haryana, India. STCS is one of the couple of high schools in Karnal with excellent standards of education provided by a Christian convent-run organization, based in Mangalore. The school was started in 1961 and has been constantly renovated. As of the 2007-08 school year, the school had an enrollment of over 3500 students and employs 100 classroom teachers.