Mater Christi Diocesan High School was founded in 1961 through the efforts of Brian J. McEntegart, then the Bishop of Brooklyn. It had separate boys' and girls' divisions which were staffed by De La Salle Brothers and Sisters of Mercy respectively. In 1974 the divisions were merged to become a fully coeducational school. In 1977 it was turned over to a community-based board of trustees and became known as Mater Christi Catholic High School. The school motto was "Ut vitam habeant et abundantius " from the Gospel of John 10:10, "That They May Have Life More Abundantly." In 1980 the school announced an affiliation with St. John's University. St. John's Prep's charter was re-issued and Mater Christi became St. John's Preparatory School.