Lasalle Higher Secondary School, which was earlier known as P.M. Ornellas High School, was started by the Portuguese Missionaries in 1875. In 1964 the Brothers took over the School after the request of Bishop Thomas Fernando. It is situated on the coastal area of bay of Bengal at Tuticorin. Once the Brothers took over the school, it was upgraded as High School. The Students who used to come to this school were from the fisherman houses, nearby slums and dropouts from other schools. So the academic standard was very poor. Then standard of the school was slowly improved due to much hard work of the Brothers.

In 1976 the Brothers started a destitute home for 100 students which is partly helped by the government. In 1984 a new hostel building was built for the poor and orphan students that has been taking care of about 200 students every year. In 1994 the name 'P.M. Ornellas' was changed as St. Lasalle High school. And in 1995 the school was upgraded as Higher Secondary School having students upto 12th standard. And in 1998 the School achieved 100% pass in the state level higher secondary government examination. During the academic years 1998-1999 the Brothers started parallel English Medium sections. In order to take care of the drop out students the Brothers also started Lasalle Vocational Training Centre offering Air Condition & Refrigeration course and Lasalle Computer Academy.