Complex sentence: The boys attended "St. Joe Prep", as the school was affectionately called, while girls continued at Bethlehem and its first high school graduating class was in 1913.
Split into simpler sentences: The boys attended "St. Joe Prep", as the school was affectionately called, while girls continued at Bethlehem to complete their schooling. Bethlehem's first high school graduating class was in 1913.