Complex sentence: In 1996-1997, the current high school was attached south of the Brown Building at 810 North Sycamore Street, then former 1923 high school across the street was demolished.
Split into simpler sentences: In 1996-1997, the current high school was built (and attached) to the south side the existing Brown Building at 810 North Sycamore Street. The former 1923 high school across the street was demolished.