Complex sentence: The school opened in the fall of 1964 with 189 male students, the first classes of Archbishop Mitty were held on the grounds of the adjacent Queen of Apostles Elementary School, but moved to the newly-completed high school buildings in April 1965.
Split into simpler sentences: The school opened in the fall of 1964 with 189 male students. The first classes of Archbishop Mitty were held on the grounds of the adjacent Queen of Apostles Elementary School, but moved to the newly completed high school buildings in April 1965.