Some of his high school years included poor grades, late nights, issues with drinking and marijuana, and a few car accidents.

[4] Diebel's mother, who hoped for the best but was well aware of Nelson's behavioral issues, arranged for him to attend the Peddie School in Hightstown, New Jersey beginning in December, 1986, where the 16-year old would swim under talented first year Head Coach Chris Martin.

[5][6] Only six months after arriving at Peddie, Diebel won a national championship, and a year later made it to the finals of the 1988 Olympic trials in the 100 and 200 breaststroke.

A repetitive stress injury in his High School Senior year due to poor technique left him the option of surgery, or toughing it out for the rigorous training required for the Olympic trials.

[4] As a Peddie senior, Nelson won three Eastern titles, setting the National High School record in the 100 yard breaststroke.

[1] Training hard for the Olympics, in March 1992, he swam a 54.48 for the 100-meter freestyle, setting the American record, but adding stress to his body.

[4] While preparing for the 1992 trials during his Freshman year at Princeton, Diebel did less well absent the motivating force that his former coach Chris Martin had provided.

[4][1] Afterward, he swam the breaststroke leg for the winning U.S. team in the men's 4×100-meter medley relay, together with fellow Americans Jeff Rouse (backstroke), Pablo Morales (butterfly) and Jon Olsen (freestyle).

He had chosen Princeton for the quality of their academic program, and because Coach Orr allowed him the flexibility of training for the more competitive meets required of an elite Olympic candidate.