Complex sentence: First opened for enrollment in 1959, the athletic mascot of West Leyden High School was the Knights until 1981, when East and West high school athletic programs merged to create one athletic team known as the Eagles.
Split into simpler sentences: First opened for enrollment in 1959, the athletic mascot of West Leyden High School was originally the Knights until 1981. At this time, the East and West Leyden High School athletic programs merged together to create an athletic team currently known as the Eagles.