Complex sentence: Originally, the new school was designed to hold roughly 750 students; from 1998-2000, the area of the grounds was increased by about 12,000 square feet in order to accommodate a larger student body and staff.
Split into simpler sentences: Originally, the new school was designed to hold roughly 750 students; in a few years, however, that number needed to be increased. During the years 1998-2000, the area of the grounds was increased by about 12,000 square feet in order to accommodate the entire student body and staff.