Complex sentence: Over the course of a few decades, more grades were added and the first and only class graduated from the Independent Presbyterian Day School in 1978, and is considered to be St. Andrew's' first alumni, consisting of 10 students.
Split into simpler sentences: Over the course of a few decades, more grades were added. The first and only class graduated from the Independent Presbyterian Day School in 1978, and is considered to be St. Andrew's' first alumni, consisting of 10 students.