In the fall of 1954, Reider gained notice in his freshman year by spearheading Harvard to its first unbeaten cross country season since 1939, with the season ending with the Big Three Meet in New Haven. Despite the fact that the course was turned into a quagmire by heavy rains, Pete broke the course record by nine seconds. In the fall of 1955, he again won the Big Three Meet, although he has to do most of his training for he meet after 10 o'clock because he was a pre-med major, and his class schedule didn't allow him to practice with the rest of the team. Called "one of the toughest little men I have ever known" by coach Bill McGurdy, he considered fatigue a mortal enemy. As a senior, he was unable to practice for three weeks prior to the Big Three Meet, but he outsprinted Yale's top two runners, fell going to the finish line, and recovered to win by 15 yards. In March of 1957, he broke Harvard's two mile record; he also ran a 9:21.7 in the IC4A meet in March of 1958. In March of 1957 at a triangular meet vs. Cornell and Penn in Philadelphia, he set a new Harvard record in the mile at 4:11, and less than an hour later, won the two mile as his dad watched him for the first time as a collegian.