The school's original construction was delayed, so for the first semester of the 1972–73 school year students attended classes at the Longmont High School building after regular hours. Niwot High School was finished on December 22, 1972. The first class of students was given the honor to choose the school's colors, mascot, and motto. These were two students from each class that was to attend the new school. The colors were kelly green and silver, the mascot was a cougar named "Carrie", and the motto was "Our Pride is Our Life". There were no seniors in the first year because the district did not want to remove current seniors from their home schools to finish their final year in a new school. Thus, the class of 1974 was the first graduating class, and the class of 1976 was the first to have been at Niwot for all four years. The football and baseball team won the conference championship their second year.