Complex sentence: At midterm of the 1966 school year, the new Waycross High school was completed and moved into during Christmas break, thus 1967 was the first class at the new Waycross High School which later became a middle school.
Split into simpler sentences: At midterm of the 1966 school year, the new Waycross High School was completed and moved into during Christmas break. Thus 1967 was the first year at the new Waycross High School, which later became a middle school.