Complex sentence: DISD began to take in WHISD-zoned students during the 2005-2006 school year, and at that time the entire Wilmer-Hutchins High School senior class attended South Oak Cliff.
Split into simpler sentences: DISD began to take in WHISD-zoned students during the 2005-2006 school year. The entire Wilmer-Hutchins High School senior class attended South Oak Cliff.