A much-anticipated event in the lives of seniors and sixth graders, the Cat Rat tradition provides a welcome to the newest members of the GPS student body.
Seniors ease the journey for sixth graders into the new GPS traditions and surroundings; sometimes lasting bonds of friendship result. Seniors and sixth graders participate in a retreat at Alpine Camp that is filled with art projects, ropes course challenges, and camaraderie. A themed parade at the beginning of the school year introduces the sixth grade rats to the student body. Past parade themes have included cartoons and television shows from the 80s.
Other activities include two luncheons hosted by the sixth graders for their senior "cats" and an ice cream social or dance sponsored by the seniors for their sixth grade "rats."

A sixth grade "rat" and a 12th grade "cat" were paired up for the 2008-09 school year by identifying socks with matching designs. These bumblebee socks were typical of the creativity and originality found in the senior class.